0IOLOGY 

LIBRARY 

G 


TWENTIETH   CENTURY  TEXT-BOOKS 


TEXT-BOOKS    IN    BOTANY 

By  John  M.  Coulter,  Ph.D. 

HEAD  OF  DEPARTMENT  OF  BOTANY  IN  THE  UNIVERSITY 
OF  CHICAGO 


Elementary  Studies  in  Botany.  Part  I, 
Plants  in  General;  Part  II,  Plants  in  Culti- 
vation. 12mo,  Illustrated,  Cloth  .  .  $1.30 

A  Text-Book  of  Botany.  12mo,  Illus- 
trated, Cloth $1.25 

Plant  Studies.  An  Elementary  Botany.  12mo, 
Cloth $1.25 

Plant  Relations.  A  First  Book  of  Botany. 
12mo,  Cloth $1.10 

Plant  Structures.  A  Second  Book  of  Bot- 
any. 12mo,  Cloth $1.20 

Plants.  The  two  foregoing  in  one  volume. 
'For  Normal  Schools  and  Colleges.  12mo, 
Cloth $1.80 

In  the  Twentieth  Century  Series  of  Text-Books 
D.  Appleton  and  Company,  New  York 

*87 


TWENTIETH   CENTURY  TEXT-BOOKS 


ELEMENTARY   STUDIES 
IN   BOTANY 


BY 


JOHN   M.   COULTER,  A.M.,  PH.D, 

HEAD   OF  THE    DEPARTMENT   OF    BOTANY 
UNIVERSITY  OF   CHICAGO 


D.    APPLETON    AND    COMPANY 

NEW  YORK  CHICAGO 


BIOLOGY 
R 
G 


COPYRIGHT,  1913,  BY 
D.  APPLETON   AND   COMPANY 


PREFACE 

IT  is  seven  years  since  A  Text-book  of  Botany  was  published, 
and  during  this  period  there  has  been  not  only  great  progress 
in  the  knowledge  of  plants,  but  also  much  discussion  con- 
cerning the  effective  use  of  plants  in  a  high  school  education. 
It  is  natural  that  a  discussion  of  this  kind  should  lead  to 
considerable  diversity  of  opinion,  and  it  is  evident  that  no 
one  is  in  a  position  as  yet  to  decide  the  points  at  issue. 
Amid  all  the  flux  of  opinion,  however,  there  is  evident  a 
desire  to  relate  plants  more  closely  to  the  interest  and  to  the 
need  of  high  school  students.  This  desire  expresses  itself  in 
an  extreme  form  when  courses  in  "  agriculture  "  are  asked  to 
be  substituted  for  courses  in  "  botany."  This  has  brought  a 
distinct  temptation  to  publishers  and  to  authors  to  "  meet 
the  demand  "  without  much  consideration  as  to  its  signifi- 
cance. It  cannot  mean  that  all  that  has  proved  good  in  the 
older  method  is  to  be  abandoned,  and  an  unorganized  mass 
of  new  material  substituted  for  it.  It  cannot  mean  that 
high  school  pupils  are  to  become  apprentices  rather  than 
students.  It  must  mean  that  the  structure  and  work  of 
plants  are  to  be  so  studied  that  this  knowledge  will  enable 
the  student  to  work  with  plants  intelligently.  In  other 
words,  it  is  intended  to  be  the  practical  application  of  knowl- 
edge, rather  than  practical  work  without  knowledge. 

The  present  book,  Elementary  Studies  in  Botany,  comprises 
two  parts,  intended  to  meet  the  two  needs  indicated  above. 

Part  I,  Plants  in  general,  gives  an  account  of  the  structure 
and  work  of  plants  simple  enough  to  be  understood  by  high 
school  students  of  any  grade,  and  brief  enough  to  be  com- 


vi  PREFACE 

pleted  in  a  half  year.  At  the  same  time,  illustrations  are 
taken  from  economic  plants,  and  practical  applications  in  the 
handling  of  plants  are  suggested.  In  other  words,  this  part 
is  intended  to  develop  some  real  knowledge  of  plants  in  con- 
nection with  a  practical  outlook.  In  telling  the  story  of 
plants,  advantage  is  taken  of  the  evolutionary  point  of  view 
merely  as  a  teaching  device.  This  method  of  presentation 
has  been  very  efficient  in  securing  a  grasp  of  the  most  impor- 
tant facts  and  in  developing  a  perspective  that  lays  emphasis 
where  emphasis  belongs. 

Part  II,  Plants  in  cultivation,  gives  an  account  of  the  prac- 
tical handling  of  plants  in  the  field  and  in  the  garden,  so  far 
as  this  can  be  accomplished  in  a  half  year  of  work.  It  is 
the  application  to  practice  of  the  knowledge  developed  in 
connection  with  the  work  outlined  in  Part  I.  The  great 
variety  of  crops  and  of  cultural  conditions  forbids  a  series  of 
specific  directions  in  reference  to  even  the  principal  crops. 
Even  if  this  were  possible,  it  would  result  in  a  series  of  direc- 
tions resembling  the  recipes  of  a  cookbook,  some  of  them 
applicable  in  one  locality  and  some  in  another,  which  is  very 
far  removed  from  the  idea  of  a  text-book.  The  plan  is  to 
develop  some  experience  in  handling  the  conditions  that 
affect  plants,  so  that  any  plant  may  be  cultivated,  in  its 
appropriate  conditions,  with  some  knowledge  of  the  things 
that  must  be  done. 

In  case  only  a  half  year  is  given  to  Botany,  Part  I  is  rec- 
ommended for  use.  It  is  complete  in  itself  and  represents 
the  real  basis  for  further  progress.  It  will  be  possible  to  use 
Part  II  alone  for  a  half  year  course,  but  the  reasons  for  the 
practice  involved  will  not  be  so  evident  as  when  it  follows 
Part  I.  The  two  parts  taken  together  represent  a  full  year 
of  work,  which  should  combine  the  demand  for  training  in 
science  with  that  of  training  in  the  culture  of  plants. 

Neither  of  the  parts  will  serve  its  purpose  unless  it  is  used 
as  a  supplement  to  the  teacher,  to  the  laboratory,  to  the 


PREFACE  vil 

experimental  garden,  and  to  field-work.  Furthermore,  it 
it  must  be  insisted  that  the  sequence  of  each  of  the  parts 
need  not  be  the  sequence  used  by  the  teacher.  For  example, 
in  Part  I,  work  on  leaves,  stems,  roots,  and  seeds  may  come 
first,  to  be  followed  by  the  general  story  of  the  plant 
kingdom.  The  sequence  may  well  differ  according  to  the 
availability  of  material  or  the  conviction  of  the  teacher. 

In  the  laboratory  work,  it  is  recommended  that  the  indi- 
vidual work  of  the  pupils  be  concerned  with  the  gross  struct- 
ures and  behavior  of  plants  chiefly,  reserving  for  occasional 
demonstration  such  structures  as  must  be  seen  under  the 
compound  microscope.  It  is  not  necessary  that  the  actual 
forms  referred  to  in  the  book  be  obtained  in  every  case. 
The  plant  kingdom  is  represented  in  every  neighborhood, 
and  it  is  far  better  to  become  acquainted  with  some  of  the 
local  algae,  fungi,  liverworts,  mosses,  etc.,  than  to  send  for 
material  that  does  not  belong  to  the  possible  experience  of 
the  student.  In  the  study  of  Seed-plants,  and  of  course  in 
Part  II,  it  is  necessary  to  arrange  for  the  growing  of  plants 
under  observation,  and  the  plants  selected  should  be  those 
ordinarily  used  in  gardens  or  fields,  especially  those  that 
germinate  quickly. 

The  illustrations  have  been  cared  for  by  my  colleague, 
Dr.  W.  J.  G.  Land,  and  unless  otherwise  credited,  all 
illustrations  have  been  prepared  for  this  volume  or  its 
predecessors. 

JOHN  M.  COULTER. 


CHAPTER 
I. 

CONTENTS 

PART   I 

PAGE 

1 

II. 

g 

III. 

FOOD  MANUFACTURE         

.      31 

IV. 

40 

V. 

BRYOPHYTES       

.      66 

VI. 

PTERIDOPHYTES          

.      88 

VII. 

SPERMATOPHYTES.     1.   GYMNOSPERMS 

.     114 

VIII. 

SPERMATOPHYTES.     2.   ANGIOSPERMS 

.     129 

IX. 

THE  FLOWER  AND  INSECT-POLLINATION 

.     151 

X. 

DISPERSAL  AND  GERMINATION  OF  SEEDS 

.     167 

LEAVES       ......... 

.    18? 

XII. 

STEMS          

.    224 

XIII. 

ROOTS          

.    253 

XIV. 

PLANT  ASSOCIATIONS         

.    272 

PART   II 

I. 

INTRODUCTION    

.    295 

II. 

WHAT  PLANTS  NEED        .        .        .        .        .        . 

.    300 

III. 

WHAT  THE  SOIL  SUPPLIES       

.    308 

IV. 

SEEDS          

.    317 

V. 

OTHER  METHODS  OF  PROPAGATION 

.    326 

VI. 

PLANT-BREEDING       

.    333 

VII. 

CEREALS  AND  FORAGE  PLANTS        .... 

.    342 

VIII. 

VEGETABLES       

.    367 

IX. 

FRUITS        

.    387 

X. 

FLOWERS     

.    401 

XL 

FIBER  PLANTS    

.     411 

XII. 

FORESTRY  ......... 

.     419 

XIII. 

432 

INDEX  . 

455 

PART   I 
PLANTS    IN   GENERAL 


CHAPTER   I 
INTRODUCTION 

1.  Occurrence  in  plants.  —  Plants  form  the  natural  cover- 
ing of  the  earth's  surface.     So  generally  is  this  true  that 
a  land  surface  without  plants  seems  remarkable.     Not  only 
do  plants   cover   the   land,  but  they  abound  in  waters  as 
well,   both  fresh   and   salt.      One   of  the   most   noticeable 
facts  in  regard  to  the  occurrence  of  plants  is  that  they  do 
not  form  a  monotonous  covering  for  the  earth's  surface, 
but  there  are  forests  in  one  place,   meadows  in  another, 
swamp  vegetation  in  another,  etc.     In  this  way  the  general 
appearance  of  vegetation  is  exceedingly  varied,  and  each 
appearance  tells  of  certain  conditions  of  living.     Such  plants 
as  appear  to  the  casual  observer  in  a  landscape  or  in  a  cul- 
tivated field  are  by  no  means  the  only  plants.     They  are 
simply   the   most   obvious   or   the  most  useful   plants,  but 
associated  with  them  are  hosts  of  plants  simpler  in  struc- 
ture and  smaller  in  size,  grading  down  to  forms  so  small 
that    they    are    visible   only  through    a    microscope.     Any 
general  view  of  the  plant  kingdom  must  include  all  plants. 

2.  Plants   as   living   things.  —  It    is    very   important    to 
begin  the  study  of  plants  with  the  knowledge  that  they  are 
alive  and  at  work.     It  must  not  be  thought  that  animals 
are  alive  and  plants  are  not.     There  is  a  common  impres- 
sion that  to  be  alive  means  to  have  the  power  of  locomotion, 
but  this  is  far  from  true ;   and  in  fact  some  plants  have  the 
power  of  locomotion  while  some  animals  do  not.     Both  plants 
and  animals  are  living  forms,  and  the  laws  of  living  that 
animals  obey  must  be  obeyed  also  by  plants.     It  is  for  this 
reason  that  the  term  biology  (the  science  that  deals  with 

1 


STUDIES  IN   BOTANY 

living  things)  applies  to  both  plants  and  animals.  There 
is  so  much  confusion  in  the  use  of  this  word  that  it  should 
be  understood  at  the  outset  that  biology  deals  with  all 
living  things,  and  that  plants  and  animals  are  two  groups 
of  living  things.  To  begin  with  the  thought  that  plants 
are  alive  and  at  work  is  important,  because  this  fact  gives 
meaning  to  their  forms  and  structures  and  positions.  For 
example,  the  form  and  structure  and  position  of  a  leaf  have 
no  -meaning  until  it  is  discovered  how  these  things  enable 
the  leaf  to  do  its  work. 

3.  Plants  and  human  needs.  —  It   is   evident   that   the 
material  welfare  of  the  human  race  is  largely  based  upon  the 
work  of  plants.     Not  only  do  they  furnish  the  fundamental 
food  supply  for  all  living  things,  but  in  innumerable  minor 
ways  they  contribute  to  the  necessities  of  human  life.     This 
important  relation  to  human  needs  has  resulted  in  grouping 
plants  into  those  that  are  useful  and  those  that  are  not, 
the  inference  often  being  that  the  latter  are  not  so  im- 
portant for  study  as  the  former.     If  useful  plants  are  to  be 
made  to  yield  the  largest  returns  under  cultivation,  it  is 
absolutely    necessary    to    understand    their    structure    and 
work.     It  is  also  true  that  plants  can  explain  one  another, 
and  many  " useless"  plants  can  interpret  useful  ones.     As  a 
rule,  the  simpler  plants  are  not  used  by  man,  but  they  are 
necessary  to  explain  the  more  complex  ones  that  he  does 
use.     It  is  further  true  that  the  scientific  study  of  plants, 
whether  useful  plants  or  not,  suggests  methods  of  making 
useful  plants  more  useful.     For  example,  the  practical  work 
of  agriculture  can  be  improved  only  as  the  scientific  work 
with  plants  points  out  the  way.     The  most  effective  way 
to  study  useful  plants,  therefore,  is  to  study  the  structure 
and  work  of  plants  in  general. 

4.  Plant  work.  —  Although  many  different  kinds  of  work 
are  being  carried  on  by  plants,  all  the  work  may  be  put 
under  two  heads :  nutrition  and  reproduction.     This  means 


INTRODUCTION  3 

that  every  plant  cares  for  two  things :  (1)  the  support  of 
its  own  body  (nutrition),  and  (2)  the  production  of  other 
plants  like  itself  (reproduction).  In  the  cultivation  of 
plants  nothing  is  so  important  as  to  know  about  their  nu- 
trition and  reproduction.  Knowledge  of  the  nutrition  of 
plants  enables  one  to  secure  vigorous  plant  bodies,  and 
knowledge  of  the  reproduction  of  plants  enables  one  to 
secure  desirable  races  of  plants.  Most  cultivators  of  plants 
follow  rules  that  they  do  not  understand,  but  to  learn  such 
rules  without  learning  plants  makes  one  an  apprentice 
rather  than  a  student. 

5.  Various  aspects  of  plants.  —  Plants  are  studied  from 
numerous  points  of  view,  so  that  botanists  are  divided  into 
many  groups.  The  oldest  subject  of  study  was  the  classi- 
fication of  plants,  which  means  discovering  their  relation- 
ships, assigning  them  to  natural  groups,  and  giving  them 
names  by  which  they  may  be  recognized.  In  human  society, 
such  a  study  would  be  the  recognition  of  family  relation- 
ships, the  grouping  of  people  by  families,  and  the  use  of 
names  to  distinguish  individuals.  Just  as  individuals  are 
distinguished  by  two  names,  so  two  names  are  given  to 
^ach  kind  of  plant,  and  Quercus  alba  (white  oak)  is  the  name 
of  a  plant,  just  as  John  Smith  is  the  name  of  an  individual. 
Plants  differ  from  human  individuals,  however,  in  that  they 
have  no  family  records,  so  that  botanists  are  compelled  to 
trust  to  certain  resemblances  to  indicate  the  family  connec- 
tions. This  means  that  plant  classification  must  change  as 
the  knowledge  of  resemblances  and  differences  increases,  so 
that  the  work  of  classification  demands  continuous  attention. 

A  second  subject  of  study  is  the  structure  of  plants.  At 
first  only  such  structures  were  included  as  could  be  seen 
with  the  naked  eye ;  but  with  the  invention  and  improve- 
ment of  the  microscope,  the  minute  structures  came  to  be 
studied  also,  so  that  it  was  possible  to  know  how  the  body 
of  a  plant  is  made.  This  led  later  to  a  study  of  how  the 


4  ELEMENTARY  STUDIES  IN  BOTANY 

body  of  a  plant  develops,  from  the  egg  to  the  adult;  and 
still  later  to  conclusions  as  to  how  plants  develop  from  one 
another,  a  subject  which  is  called  evolution.  If  the  classifi- 
cation of  plants  is  likened  to  the  recognition  of  the  family 
connections  and  the  names  of  people,  the  study  of  the 
structure  of  plants  may  be  likened  to  the  study  of  the  struc- 
ture of  the  human  body  and  the  details  of  its  development 
from  the  egg  to  the  adult. 

A  third  subject  of  study  is  the  work  of  plants.  It  must 
be  remembered  that  plants  are  living  things  that  use  food, 
grow,  and  reproduce,  and  all  this  means  the  work  of  a  liv- 
ing body.  The  study  of  the  structure  of  plants  is  like  the 
study  of  the  parts  of  an  engine  and  how  they  are  put  together, 
but  the  study  of  the  work  of  plants  is  like  the  study  of  the 
engine  in  action.  It  is  evident  that  a  study  of  the  structures 
of  plants  finds  its  meaning  in  helping  one  to  understand  the 
activities  of  plants,  just  as  a  study  of  the  structure  of  the 
human  body  finds  its  motive  in  helping  one  to  understand 
the  human  body  alive  and  doing  its  work. 

A  fourth  subject  of  study  is  the  diseases  of  plants,  which 
often  ravage  our  crops.  The  chief  causes  of  these  diseases 
are  other  plants,  so  that  this  study  involves  a  knowledge 
of  the  structure  of  two  sets  of  plants,  those  that  attack  and 
those  that  are  attacked.  In  addition  to  this,  it  involves 
a  knowledge  of  two  kinds  of  work,  the  work  of  the  plant 
when  in  health  and  its  work  when  diseased.  The  study 
of  plant  diseases  is  regarded  as  a  very  practical  one,  but  it 
is  evident  that  it  cannot  be  carried  on  effectively  without 
a  previous  knowledge  of  the  structure  and  work  of  plants. 
Among  the  plants  that  induce  disease  in  other  plants  are 
the  bacteria,  which  are  also  conspicuous  in  causing  certain 
diseases  among  human  beings.  These  minute  and  peculiar 
plants  require  such  special  treatment  for  their  study  that 
they  form  a  subject  by  themselves  and  demand  a  specially 
trained  group  of  botanists. 


INTRODUCTION  5 

A  fifth  subject  of  study  is  the  life-relations  of  plants. 
Plants  become  related  effectively  to  such  things  outside 
of  themselves  as  light,  water,  soil,  and  other  plants,  and 
how  this  is  accomplished  is  the  subject  referred  to.  Plants 
may  be  studied  as  individuals  relating  themselves  to  their 
surroundings,  just  as  a  human  individual  may  be  studied 
as  he  adjusts  himself  to  the  conditions  of  life  in  a  city;  or 
they  may  be  studied  in  "  vegetation  masses,"  such  as 
forests  or  prairies,  just  as  groups  of  people  in  a  city  may 
be  studied  as  they  adjust  themselves  to  other  groups. 
One  great  natural  vegetation  mass  is  of  such  practical 
importance  that  it  has  developed  the  special  subject  of 
forestry. 

A  sixth  subject  is  known  as  plant-breeding,  and  it  has 
become  of  great  scientific  and  practical  importance.  It 
means  the  growing  of  plants,  generation  after  generation, 
under  observation  and  control,  and  trying  to  discover  the 
laws  of  inheritance,  which  we  usually  call  heredity.  This 
is  the  great  scientific  importance  of  plant-breeding.  Its 
practical  importance  comes  from  the  fact  that  the  scien- 
tific work  has  suggested  methods  of  improving  our  old  plants, 
producing  new  ones,  and  guarding  our  crops  against  disease 
and  drought.  From  the  standpoint  of  our  material  in- 
terests nothing  can  be  more  important,  for  it  lies  at  the  basis 
of  the  world's  food  supply. 

The  six  aspects  of  plants  described  above  do  not  exhaust 
the  list,  but  they  are  conspicuous  illustrations  of  the  fact 
that  botany  is  not  a  single  study,  but  includes  many  kinds 
of  study. 

6.  Simple  and  complex  plants.  —  Plants  differ  greatly 
not  only  in  size,  from  microscopic  forms  to  huge  trees,  but 
also  in  complexity  of  structure.  Some  plants  are  so  simple 
that  all  regions  of  the  body  are  alike,  while  others  are  so 
complex  that  the  body  consists  of  many  kinds  of  structures. 
Although  the  structure  of  simple  and  complex  plants  is 
2 


6  ELEMENTARY  STUDIES  IN  BOTANY 

very  different,  they  do  the  same  kinds  of  work.  The 
work  does  not  become  more  complex,  but  the  structures 
developed  to  do  it  become  more  complex. 

It  is  believed  that  the  simple  plants  were  the  first  mem- 
bers of  the  plant  kingdom,  and  that  plants  gradually  be- 
came more  and  more  complex  until  the  structure  of  our 
highest  plants  was  reached.  To  understand  the  structure 
of  the  higher  plants,  it  is  necessary,  therefore,  to  approach 
it  as  plants  approached  it,  by  beginning  with  simple  forms 
and  noting  the  appearance  of  one  change  after  another 
until  the  greatest  complexity  is  reached.  It  happens  that 
the  plants  we  use  most  are  most  complex,  and  therefore 
the  tendency  has  been  to  study  them  first  and  often  to 
study  them  only;  but  we  are  assuming  in  this  book  that 
a  study  of  plants  is  intended  to  develop  some  real  knowl- 
edge of  plants. 

Therefore,  in  the  following  pages  we  will  begin  with  the 
simplest  plants,  and  discover  how  the  plant  kingdom  gradu- 
ally became  what  it  is.  In  this  way  we  shall  really  know 
something  of  the  structure  and  work  of  the  plants  we  use 
most. 

7.  The  four  great  groups.  —  It  is  customary  to  divide 
the  plant  kingdom  into  four  great  groups.  These  groups 
proceed  from  the  simplest  to  the  most  complex  plants, 
so  that  it  will  be  helpful  to  obtain  a  glimpse  of  them  in 
advance,  as  this  will  explain  the  order  in  which  the  plants 
are  presented. 

(1)  Thallophytes.  —  These  are  the  simplest  plants,  and 
therefore  the  lowest  group.  The  name  means  "thallus- 
plants,"  and  a  thallus  is  a  simple  kind  of  plant  body  which 
will  be  understood  when  it  is  met.  The  conspicuous  mem- 
bers of  this  group  are  called  Algae  and  Fungi,  the  former 
being  the  " seaweeds/'  although  many  of  them  live  in 
fresh  water,  and  the  latter  including  such  forms  as  mush- 
rooms among  their  higher  members. 


INTRODUCTION  7 

(2)  Bryophytes.  —  These    are    the    first    plants    that    in- 
habited the  land  surface.     The  name  means  "  moss-plants," 
for  the  mosses  are  the  most  numerous  representatives  of  the 
group. 

(3)  Pteridophytes.  —  These  are  the  first  plants  that  de- 
veloped a  woody  system.     The  name  means  " fern-plants," 
for  the  ferns  are  the  most  numerous  representatives  of  the 
group. 

(4)  Spermatophytes.  —  This     highest     group     developed 
seeds,  and  the  name  means  " seed-plants."     Most  of  them 
also    developed    flowers,    and    they    are    sometimes    called 
" flowering  plants."     It  is  the  seed-plants  that  man  uses 
most,  but  to  understand  and  explain  them,  one  must  know 
the  other  groups. 


'      CHAPTER   II 
THALLOPHYTES.  —  1. 

THE  PRIMITIVE  PLANTS 

8.  Definition.  —  Algae   are   called    the   primitive   plants 
because  they  are  thought  to  have  preceded  the  other  groups 
historically.     This  does  not  mean  that  they  were  neces- 
sarily the  first  plants,  for  plants  that  have  disappeared,  or 
that  we  have  failed  to  recognize,  may  have  preceded  the 
Algae.     But  in  our  present  flora,  as  an  assemblage  of  plants 
is  called,  the  Algae  appear  to  be  the  forms  that  have  given 
rise  to  the  other  groups.     They  are  comparatively  very 
simple,  but  not  necessarily  very  small,  for  certain  seaweeds 
become  as  bulky  as  do  the  higher  plants. 

The  Algse  are  of  very  little  practical  importance,  hence 
their  study  is  not  due  to  the  fact  that  men  use  them.  But 
they  are  of  very  great  scientific  importance,  because  they 
illustrate  the  beginnings  of  the  plant  kingdom,  and  show 
how  the  important  kinds  of  plant  work  are  provided  for  in 
the  simplest  way.  They  are,  in  fact,  a  simple  introduction 
to  the  study  of  plants. 

9.  Water  as  a  medium.  —  If  Alga?    are  the  primitive 
plants,  it  follows  that  the  plant  kingdom  began  in  the  water, 
for  Algae  grow  in  water  or  in  very ^  moi_st_places.     It  seems 
to  be  true,  also,  that  the  most  primitive  Algae,  as  well  as 
those  that  gave  rise  to  the  higher  plants,  lived  in  fresh 
water ;   so  that  the  numerous  Algae  that  live  along  the  sea- 
coasts  are  not  the  most  primitive,  nor  have  they  given  rise 
to  higher  plants.     From  this  point  of  view,  it  follows  that 
the  fresh  water  Algae  are  the  most  important  to  study. 

8 


THALLOPHYTES 


9 


To  live  in  water  as  a  medium  means  that  all  the  structures 
and  habits  of  such  plants  must  be  adjusted  to  water. 
Such  plants  can  be  explained  only  by  remembering  this 
fact.  That  plants  living  in  the  water  may  be  relatively 
simple  is  illustrated  by  the  fact  that  when  plants  live  in 
the  air  they  must  be  protected  against  drying,  and  this  in- 
volves protective  structures  that  water  plants  do  not  need. 

10.  The  cell  (Fig.  1).  — The  living 
substance  of  plants  and  animals  is 
called  protoplasm.  It  is  the  only  sub- 
stance that  lives  and  works,  and  all 
the  structures  and  work  of  plants 
are  results  of  the  activity  of  pro- 
toplasm. This  protoplasm  is  organ- 
ized into  definite  units,  which  may 
be  thought  of  as  protoplasm  indi- 
viduals, and  these  units  or  individuals 
are  the  cells.  The  simplest  plants 
are  single  cells,  while  large  and  com- 
plex plants  consist  of  millions  of  cells. 
It  is  in  this  sense  that  a  cell  may  FlG-  1.  —  Ceiis.of  a  moss 

leaf:  in  each  of  the   two 

be  called  the  unit  of  structure,  and 
that  a  plant  consisting  of  one  such 
unit  may  be  regarded  as  the  simplest 
kind  of  plant. 

Since   a   cell   always  includes  sub- 

*.  stances  that  are  not  protoplasm,  the  term  protoplast  is 
used  to  indicate  the  living  substance  of  the  cell.  The 
protoplast,  therefore,  is  the  living,  individual  unit,  and 
protoplasm  is  the  material  of  which  it  is  composed.  We 
shall  use  the  term  protoplast,  therefore,  for  the  living, 
protoplasmic  individual. 

Among   plants,    the   semifluid    protoplast    usually   sur- 

C  rounds  itself  with  a  wall  (Fig.  1).  This  cell-wall  is  com- 
posed of  material  called  cellulose,  which  is  manufactured 


complete  cells  the  single 
large  nucleus  is  seen,  the 
numerous  chloroplasts, 
and  the  granular-looking 
cytoplasm ;  the  cell-wall 
surrounding  each  cell  is 
very  distinct. 


10  ELEMENTARY   STUDIES  IN  BOTANY 

by  the  protoplast,  and  which  forms  a  delicate  but  tough  and 
elastic  layer. 

The  protoplast  within  its  cell-wall  is  a  very  complex 
structure,  which  does  a  great  variety  of  work.  There  are 
always  at  least  two  distinct  regions  or  organs  of  the  pro- 
toplast, which  differ  in  appearance  and  in  work.  The 
^\  nucleus  is  usually  a  globular  mass  of  protoplasm  (Fig.  1), 
lying  in  the  midst  of  the  protoplast,  and  marked  off  sharply 
by  a  delicate  investing  membrane.  It  is  impossible  to 
tell  all  that  the  nucleus  does,  but  it  is  conspicuous  in  the 
work  of  cell-division,  that  is,  the  process  by  which  a  cell 
divides  and  forms  two  new  cells. 

The  remainder  of  the  body  of  the  protoplast,  in  which 
^  the  nucleus  lies  imbedded,  is  called  the  cytoplasm.  -It"  must 
not  be  thought  that  the  cytoplasm  is  just  a  mass  of  pro- 
toplasm around  the  nucleus,  for  it  has  a  structure  of  its 
own,  and  is  especially  conspicuous  in  the  general  processes 
of  nutrition,  which  means  the  chemical  and  physical 
processes  that  take  place  in  connection  with  the  use  of  food. 

In  green  plants,  such  as  the  Algae,  there  is  a  third  organ 
C  of  the  protoplast,  called  the  chloroplast  (Fig.  1).  Chloro- 
plasts  are  protoplasmic  bodies  of  various  forms  among  the 
Algae,  but  among  the  higher  plants  they  are  usually  more 
or  less  globular.  There  may  be  a  single  chloroplast  in  a  cell 
or  there  may  be  several  chloroplasts,  and  they  are  dis- 
tinguished from  the  nucleus  or  from  any  other  body  in  the 
cell  by  their  green  color,  a  color  due  to  the  presence  of 
a  green  stain  called  chlorophyll.  The  peculiar  work  of  the 
chloroplasts  is  to  manufacture  food  from  raw  material, 
the  details  of  which  are  outlined  in  the  next  chapter. 

A  very  important  fact  to  know  in  reference  to  the  cell 
is  that  the  pj*otoplast  is  saturated  with  water  when  active. 
The  water  accumulates  in  the  protoplasm,  until  the  cell 
swells  and  the  wall  becomes  stretched  and  tense.  This 
swollen  condition  of  the  cell  is  called  turgor,  and  it  is  one 


THALLOPHYTES  11 

of  the  conditions  necessary  for  its  activity.  Anything  that 
withdraws  water  from  the  cell  diminishes  its  activity,  and 
if  the  loss  of  water  continues,  the  protoplast  becomes  in- 
active and  may  pass  into  the  condition  called  dormancy. 
In  seeds,  for  example,  the  protoplasts  may  remain  in  this 
dormant  condition  for  a  long  time,  and  then  become  active 
again  when  water  is  restored. 

11.  Work  of  the  cell.  —  The  work  of  the  cell  has  been 
referred  to  in  describing  its  parts,  but  it  is  important  to 
emphasize  it.     The  work  of  a  plant  of  many  cells  is  simply 
the  sum  of  the  work  of  all  its  cells.     The  work  done  by 
a  living  cell  is  so  complex  that  it  may  be  analyzed  under 
several  heads,  but  all  of  it  may  be  grouped  under  two  heads. 

One  is  the  work  of  nutrition,  which  includes  everything 
that  has  to  do  with  the  securing  and  using  of  food.  It  is 
by  this  work  that  a  plant  maintains  itself  in  vigor  and  in 
growth.  The  principal  part  of  the  body  of  a  complex  plant 
is  concerned  with  the  work  of  nutrition,  and  this  part  is 
called  the  nutritive  or  vegetative  body  of  the  plant. 

The  other  kind  of  work  is  reproduction,  which  includes 
everything  that  has  to  do  with  producing  new  plants. 
In  most  plants  the  reproductive  structures  form  a  relatively 
small  part  of  the  body,  but  in  one-celled  plants  or  in  simple 
many-celled  plants  nutrition  and  reproduction  are  carried 
on  by  all  the  cells. 

12.  The  vegetative  body  of  Algae.  —  Algae  may  be  ar- 
ranged in  a  series,  beginning  with  those  having  the  most 
simple  bodies,   and  advancing  to  those  having  the  most 
complex  bodies.     In  this  way  one  can  appreciate  the  prog- 
ress made  by  the  plant  body,  and  also  the  amount  of  such 
progress  made  by  the  Algae.     For  the  sake  of  clearness, 
we  may  think  of  the  bodies  of  Algae  as  representing  different 
stages  of  general  progress. 

The  first  stage  is  represented  by  those  Algae  whose  bodies 
are  single  cells.  Such  plants  are  represented  in  the  illustra- 


12 


ELEMENTARY  STUDIES  IN   BOTANY 


tions  by  Pleurococcus  (Fig.  2),  very  common  as  green 
patches  on  damp  tree  trunks,  old  board  fences,  damp  walls 
and  rocks,  etc.  When  material  from  these  patches,  which 
often  look  like  green  stains,  is  observed  under  the  mi- 
croscope, it  is  discovered  to  be  made  up  of  innumerable 

green,  spherical  cells.  The  figure 
referred  to  (Fig.  2)  shows  a  sin- 
gle individual  and  also  the  suc- 
cessive divisions  that  result  in 
groups  of  individuals.  In  every 
case,  each  cell  is  a  separate  plant, 
quite  independent  of  all  the  rest. 
In  each  plant  (cell)  shown  in  the 
figure  the  nucleus  may  be  seen, 
surrounded  by  the  granular-look- 
ing cytoplasm,  and  this  in  turn 
invested  by  a  wall.  It  is  evident 
that  these  minute  individuals  are 
equipped  to  do  the  work  of  nu- 
trition and  of  reproduction  just 
as  truly  as  are  the  larger  plants. 
A  second  stage  is  represented 
by  those  Algae  whose  bodies  are 
also  single  cells,  but  the  cells  cling 


FIG.  2.  —  Pleurococcus;  in  the  up- 
per left-hand  corner  is  a  single 
plant  (one  cell),  with  its  nu- 
cleus and  cytoplasm  surrounded 
by  a  cell-wall ;  in  other  figures 
the  cell  has  divided,  and  has 
given  rise  to  loose,  irregular 
groups,  in  which  each  cell  is  an  . 

independent   individual,    and     together  in  such  definite  groups 
Jhe^eslr0"168  separated  from     that  the  groups  are  called  colo- 
nies.    Examples  of  such  plants 

are  shown  in  Figs.  3  and  4,  In  Fig.  3  (Gkeotfyece) , 
the  cells,  as  they  are  formed,  are  held  together  in  a  more 
or  less  irregular  colony  by  a  mucilage  that  is  developed 
from  the  cell- wall  material  (cellulose).  In  Fig.  4,  two- 
colonies  are  shown:  Nostoc  (A),  with  the  cells  (individ- 
uals) held  together  in  a  definite  row,  so  that  the  colony 
resembles  a  string  of  beads,  and  the  mucilage  is  so  abundant 
that  many  such  colonies  may  be  imbedded  together  in  a  single 


THALLOPHYTES 


13 


jelly-like  mass;  and  Gloeotrichia  (B),  with  its  cells  arranged 
as  in  Nostoc,  but  showing  that  the  cells  are  becoming  dif- 
ferent, so  that  the  base  and  apex  of  the  colony  are  not  alike. 
Gloeothece  (like  Pleurococcus)  is  found  in  bluish  green  patches 
on  tree  trunks,  fences,  walls,  etc. ;  and  Nostoc  occurs  as  small 
lumps  of  jelly  in  damp  places.  In  these  colonies  the  cells 
(individuals)  are  held  together  mechanically  by  the  mucilage, 
but  they  seem  to  be  as  independent  as  if  they  were  separate. 

In  the  case  of  other  colonies, 
such  as  the  one  shown  in  Fig.  5, 
the  cells  are  much  more  closely 
related,  being  pressed  against  one 
another  so  as  to  flatten  the  walls 
that  are  in  contact.  Although 
the  cells  of  this  colony  (Oscil- 
latoria)  are  for  the  most  part  in- 
dependent of  one  another,  as 
shown  by  the  fact  that  they 
may  break  apart  and  live  inde- 
pendently, they  work  together  in 
,  certain  ways,  notably  in  the  char- 
acteristic swaying  and  revolving 
movements  of  the  colony  as  a 
whole,  movements  that  have 
given  name  to  the  plant.  This  interesting  plant  forms  bluish 
green  slippery  masses  on  wet  rocks,  or  it  occurs  on  damp 
soil  or  freely  floating  on  the  water. 

When  the  individual  cells  of  a  colony  work  together  in  a 
still  more  intimate  way,  the  colony  of  many  individuals  be- 
comes the  individual  of  many  cells.  This  many-celled  in- 
dividual is  the  third  stage  in  the  progress  of  the  plant  body, 
and  it  is  evident  that  there  is  no  way  of  telling  just  when 
a  colony  becomes  such  an  individual.  The  three  general 
stages,  therefore,  are  (1)  the  single  cell,  (2)  the  colony, 
(3)  the  many-celled  individual.  All  of  the  remaining 


FIG.  3.  —  Glceothece:  in  the  upper 
left-hand  corner  is  a  single 
plant  (one  cell),  with  its  nu- 
cleus, cytoplasm,  and  wall,  and 
also  a  covering  of  mucilage  de- 
veloped from  the  wall-material 
(cellulose) ;  in  the  other  figures, 
successive  divisions  are  shown, 
resulting  in  an  irregular  colony 
of  individuals  held  together  by 
the  investing  mucilage. 


14 


ELEMENTARY    STUDIES   IN    BOTANY 


illustrations   of   the   Algse   show   examples   of   many-celled 
individuals. 

The  bodies  of  many-celled  Algse  have  different  forms, 
which  may  be  referred  to  three  general  heads.  It  has  been 
stated  that  cells  divide.  This  is  too  complicated  a  process 
to  describe  here,  but  in  general  it  means  that  the  nucleus 


FIG.  4.—  Nostoc  (A)  and  Gloeotrichia 
(B) :  the  colony  has  the  form  of  a 
beaded  filament,  imbedded  in  a 
mucilage  sheath ;  in  B  the  cells  at 
the  base  of  the  colony  are  much 
larger  than  those  above,  showing 
that  the  individual  cells  are  be- 
ginning to  differ. 


FIG.  5.  —  Oscillatoria :  a> 
very  compact  fila- 
mentous colony,  in 
which  the  cells  work 
together  to  produce 
the  oscillating  move- 
ment of  the  colony. 


divides  first  and  that  a  new  wall  is  laid  down  between  the 
two  nuclei  and  extends  through  the  cytoplasm  to  the  old  wall, 
making  two  cells  half  the  size  of  the  original  one,  just  as 
a  partition  run  through  a  room  divides  it  into  two  smaller 
rooms.  The  new  cells  differ  from  the  new  rooms,  however, 
in  growing  until  each  one  is  as  large  as  the  old  cell. 


THALLOPHYTES 


15 


FIG.  6.  —  Coleochcete:  a 
flat,  plate-like  body; 
from  such  an  alga 
body  the  land  plants 
were  probably  de- 
rived. 


In  the  first  place,  the  cells  composing  the  individual  may 
divide  freely  in  every  plane,  and  this  results  in  a  massive  body. 
This  form  is  not  very  common  among 
Algae,  because  it  is  not  the  most  favor- 
able arrangement  of  cells  for  free  ex- 
posure to  water. 

In  the  second  place,  the  cells  com- 
posing the  individual  may  divide  chiefly 
in  two  planes,  at  right  angles  to  one 
another,  and  this  results  in  a  flat,  plate- 
like  body,  which  may  be  a  single  layer 
of  cells  in  thickness,  or  several  layers 
(Fig.  6).  This  form  of  body  is  more 
favorable  for  water  exposure  than  the  massive  form,  but 
it  is  not  the  most  favorable. 

In  the  third  place, 
the  cells  composing  the 
individual  may  divide 
only  or  chiefly  in  one 
plane,  or  rather  in  a 
series  of  parallel  planes, 
and  this  results  in  a  fil- 
amentous body  (Figs. 
7,  A,  and  8).  This  is 
by  far  the  most  common 
form  of  body  among 
the  Algae,  especially  the 
fresh-water  forms,  and 
it  permits  not  only 
every  cell  to  come  into 
contact  with  water 
freely,  but  also  the  free 
swaying  movements 
that  are  of  advantage  in  water. 

Another  tendency  in  many-celled  plants,  which  results  in 


FIG.  7.  —  Ulothrix:  A,  base  of  filament,  showing 
the  holdfast  cell  and  five  of  the  ordinary  cells 
above ;  B,  four  cells  of  a  filament  containing 
spores ;  C.  showing  one  cell  (a)  containing 
four  swimming  spores,  a  free  swimming  spore 
(6),  four  escaped  gametes  (c),  pairing  gametes 
(d),  and  two  oospores  (e)  each  of  which  has 
been  produced  by  the  fusion  of  two  gametes ; 
Z>,  a  young  filament  started  by  a  swimming 
spore. 


16 


ELEMENTARY   STUDIES   IN   BOTANY 


the  development  of  increasingly  complex  bodies,  is  for  the 
cells  to  become  unlike.     This  tendency  to  become  different 


FIG.  8.  —  Cladophora: 
a  branching  fila- 
ment, each  of  whose 
cells  contains  several 
nuclei ;  in  two  of 
the  cells  swimming 
spores  have  devel- 
oped, and  from  one 
of  the  cells  some  of 
the  spores  have  es- 
caped, showing  the 
pair  of  cilia. 


FIG.  9.  —  Laminar ia :  a 
common  kelp,  show- 
ing a  complex  body 
differentiated  into 
holdfast,  stalk,  and 
blade  (leaf-like  por- 
tion). 


is  called  differentiation.     For  example,   in  the  filamentous 
body  of   Ulothrix  (Fig.  7,  A)  the  lowest  cell  differs  from  all 


FIG.  10.  —  Macrocystis:  a  kelp  with  very 
long  and  rope-like  stem  bearing  nu- 
merous blades.  —  After  BENNETT  and 
MURRAY. 


THALLOPHYTES 


17 


the  rest  in  size  and  form  and  contents,  and  serves  as  a  hold- 
fast for  anchoring  the  plant.  This  anchoring  cell  is  found 
in  a  great  many  filamentous  forms,  and 
shows  that  differentiation  of  form,  etc., 
has  to  do  with  difference  of  work.  Among 
the  marine  Alga3  this  differentiation  be- 
comes very  great.  For  example,  in  such 
seaweeds  as  are  illustrated  in  Figs.  9  to 
14,  there  are  complex  holdfasts  (often 
looking  like  roots),  stalks  (resembling 
stems),  and  leaf-like  portions  (which 
may  just  as  well  be  called  leaves).  In 
these  cases,  not  only  is  the  body  differ- 
entiated into  dif- 
ferent regions,  but 
the  cells  composing 
each  region  are  dif- 
ferentiated. 

To    summarize 
these  statements  in 

reference  to  the  vegetative  bodies  of 
AlgaB,  it  may  be  said  that  the  Algae 
begin  as  one-celled  plants  and  become 
many-celled  plants ;  that  the  cells  of 
the  many-celled  forms  become  differ- 
entiated ;  and  that  finally  the  many- 
celled  body  becomes  differentiated 
into  different  regions. 

13.  Reproduction.  —  The  preceding 
sections  give  an  account  of  the  vege- 
tative body  of  Algae.  It  now  remains 
to  consider  the  methods  of  reproduc- 
tion developed  by  the  Alga?.  It  must 
be  understood  that  reproduction  began  as  a  relatively  simple 
process,  and  that  it  became  gradually  more  and  more  com- 


FIG.  11.  —  Nereocystis : 
a  bladder  kelp,  show- 
ing the  blades  arising 
from  the  bladder-like 
expansion  of  the  end 
of  the  stalk. 


FIG.  12.  —  Fucus:  fragment 
of  rockweed,  showing  the 
forked  branching,  the 
swollen  tips  in  which  the 
sex-organs  are  produced, 
and  the  air  bladders  (three 
of  them  near  the  base). 


18 


ELEMENTARY   STUDIES   IN   BOTANY 


plex,  and  therefore  that  there  has  been  an  evolution  of  re- 
production. It  must  not  be  supposed  that  reproduction 
always  became  more  complex  as  a  vegetative  body  became 
more  complex,  for  comparatively  simple  bodies  may  show 
an  advanced  method  of  reproduction,  and  many  complex 
bodies  have  retained  a  relatively  simple  method  of  reproduc- 
tion. In  general,  however,  as  plants  advanced  in  the  struct- 
ure of  their  bodies,  they  advanced 
also  in  the  methods  of  reproduc- 
tion. 

14.  Vegetative  multiplication. 
-  In  the  simplest  plants,  notably 
the  one-celled  forms,  new  individ- 
uals arise  by  dividing  the  old  ones. 
For  example,  a  one-celled  indi- 
vidual works  for  a  time  as  a  vege- 
tative body  (engaged  in  the  work 
of  nutrition),  and  then  the  cell 
divides,  producing  two  new  indi- 
viduals (Figs.  2  and  3).  Since 
this  kind  of  reproduction  involves 

only  vegetative  cells,  it  is  called  vegetative  multiplication, 
which  means  that  it  is  simply  a  method  of  multiplying 
vegetative  cells.  When  these  multiplied  vegetative  cells  are 
new  individuals,  the  process  becomes  a  kind  of  reproduction. 
This  seems  to  have  been  the  first  kind  of  reproduction 
among  plants,  and  in  many  groups  it  is  still  the  only  kind  of 
reproduction.  Any  group  that  has  no  other  method  of  re- 
production is  regarded  as  one  of  very  low  rank,  for  the  method 
of  reproduction  among  plants  is  regarded  as  more  important 
in  ranking  them  than  is  the  structure  of  their  vegetative 
bodies. 

It  must  not  be  supposed  that  vegetative  multiplication 
occurs  only  among  the  lowest  plants,  for  it  is  found  in  all 
groups  of  plants,  even  the  highest.  For  example,  when 


FIG.  13.  —  Sargassum:  fragment 
of  gulfweed,  showing  differen- 
tiation of  the  body  into  stem, 
leaves,  and  bladder-like  floats 
(resembling  berries). 


THALLOPHYTES 


19 


potatoes  are  planted,  the  tuber,  composed  of  vegetative 
cells,  is  cut  into  pieces,  and  each  piece  can  develop  a  com- 
plete new  plant.  The  leaves  of  some  plants  can  be  used  in 
the  same  way ;  grapevines  are  usually  started  by  planting 
"  cuttings  "  or  "  slips  "  (bits  of  stem) ;  and  the  process  of 
"grafting"  fruit  trees  really  means  starting  new  individuals 


FIG.  14.  —  One  of  the  Red  Algae,  showing  a  very  much  differentiated  and  complex 

body. 

from  vegetative  structures.  When  a  new  method  of  repro- 
duction appears  among  plants,  therefore,  it  does  not  mean 
that  the  old  method  is  dropped,  but  that  the  new  one  is 
added. 

A  very  important  fact  in  reference  to  vegetable  multi- 
plication remains  to  be  stated.  When  the  cell  of  a  one-celled 
plant  divides,  the  result  is  two  new  individuals;  but  when 


20 


ELEMENTARY   STUDIES   IN   BOTANY 


a  vegetative  cell  of  a  many-celled  plant  divide's,  the  result  is 
usually  the  addition  of  new  cells  to  the  body,  so  that  there 
are  no  new  individuals,  but 
the  old  individual  grows. 
In  other  words,  the  cell- 
division  which  results  in 
reproduction  among  one- 
celled  plants  usually  re- 
sults only  in  growth  among 
many-celled  plants.  In  a 
certain  sense,  any  such 
growth  is  reproduction,  for 
new  cells  are  produced,  but 
we  are  using  the  word  re- 
production in  the  sense  of 
producing  new  individuals. 


FIG.  15.  —  (Edogonium:  A,  part  of  a  filament,  one  of  whose  cells  has  formed  a  single 
large  swimming  spore  with  a  crown  of  cilia ;  B,  part  of  a  filament  showing  antheridia 
(a)  from  which  two  sperms  (b)  have  escaped,  a  vegetative  cell  with  its  nucleus,  and 
an  oogonium  (the  large  round  cell)  filled  by  a  large  egg  packed  with  food  and  whose 
nucleus  is  seen  (d) ,  and  which  a  sperm  has  entered  (c)  ;  C,  a  swimming  spore  with  its 
crown  of  cilia ;  D,  a  young  plant  developing  from  the  swimming  spore. 

It  is  quite  evident,  therefore,  that  this  process  of  cell- 
division  goes  on  in  all  plants,  and  that  in  the  lowest  it  is 
the  only  method  of  reproduction. 


THALLOPHYTES 


21 


15.  Spore-reproduction.  —  The  second  method  of  re- 
production that  appears  among  the  Algae  is  reproduction  by 
spores.  A  spore  is  a  special  reproductive  cell,  as  distinct 
from  a  vegetative  cell.  For  example,  in  such  a  form  as 
Ulothrix  (Fig.  7),  the  vegetative  body  is  a  filament  of  cells 
(A).  These  cells  perform  the  ordinary  vegetative  work  of 
green  cells  when  the  con- 
ditions favor  such  work ; 
but  if  the  conditions 
change,  they  may  begin 
to  form  spores  (B  and 
C) .  The  protoplast  that 
has  been  doing  vegeta- 
tive work  divides,  and 
this  division  may  be  fol- 
lowed by  others,  until 
the  wall  of  the  old  vege- 
tative cell  incloses  a 
number  of  new  cells, 
which  are  the  spores. 
The  spores  escape  from 
the  old  inclosure  into 
the  water,  and  in  Ulothrix 
they  swim  freely  about 
by  means  of  a  tuft  of 
four  cilia  (hairs)  at  the 
tip  of  each  spore  (C,  6). 
These  "  swimming  spores  "  are  very  characteristic  of  the 
Algse,  but  the  number  and  arrangement  of  the  cilia  vary. 
For  example,  in  (Edogonium  (Fig.  15,  A  and  C)  the  cilia 
occur  as  a  crown  at  one  end ;  in  the  brown  seaweeds  there 
is  a  pair  of  cilia  on  one  side  of  the  spore  (Fig.  16) ;  in  certain 
forms  there  is  a  single  cilium ;  while  the  most  common  con- 
dition is  a  pair  of  cilia  at  the  apex  of  the  spore  (Fig.  8). 

It  must  not  be  supposed  that  spores  are  necessarily  ciliated, 
3 


FIG.  16.  —  Ectocarpus :  A,  part  of  a  filament 
showing  a  sporangium  distinct  from  the  vege- 
tative body,  and  also  an  escaped  swimming 
spore  (enlarged)  with  its  two  lateral  cilia ;  B, 
part  of  a  filament  showing  a  gametangium 
distinct  from  the  vegetative  body,  and  also 
an  escaped  gamete  with  its  two  lateral  cilia. 


22 


ELEMENTARY   STUDIES   IN   BOTANY 


for  spores  of  the  Red  Algge,  for  example,  have  no  cilia  (Fig. 
17)  and  are  carried  about  passively  by  the  water,  while  the 
.spores  of  higher  plants  are  carried  through  the  air.  Nor 
must  it  be  supposed  that  spores  are  necessarily  produced 
by  the  division  of  a  protoplast;  they  generally  are,  but 
sometimes  the  whole  protoplast  escapes  from  its  investing 
wall  and  is  a  spore  (Fig.  15,  A).  Nor  is  a  spore  always 
naked  (without  a  wall).  Although  swimming  spores  are 

usually  naked,  spores  exposed 
to  the  air  have  walls,  and 
sometimes  very  heavy  walls. 
A  spore  is  recognized,  there- 
fore, not  by  its  cilia,  its  form, 
its  covering,  or  its  origin,  but 
simply  from  the  fact  that  it 
is  able  to  produce  a  new 
plant.  The  process  by  which 
a  spore  starts  a  new  plant  is 
called  germination,  so  that 
the  business  of  a  spore  is  to 
germinate. 

In  most  of  the  Alga3, 
spores  are  produced  by  the 
ordinary  vegetative  cells,  that  is,  by  cells  that  are  a  part  of  the 
vegetative  body  and  form  spores  only  when  the  conditions 
for  vegetative  work  become  unfavorable.  Gradually,  among 
the  Alga3,  however,  the  cell  that  produces  spores  becomes 
more  and  more  distinct  from  the  other  cells,  until  finally 
it  is  entirely  distinct,  doing  no  vegetative  work,  and  only 
producing  spores,  as  in  the  brown  alga  shown  in  Fig.  16 
and  in  the  red  alga  shown  in  Fig.  17.  Such  a  cell  is  called 
a  sporangium,  which  means  "  spore-case."  Although  Alga3 
are  characterized  by  an  abundant  formation  of  spores,  it 
is  only  among  the  higher  groups  of  Algae  that  sporangia 
become  differentiated  from  the  rest  of  the  body. 


FIG.  17.  —  Portion  of  a  red  seaweed,  show- 
ing a  sporangium  with  its  four  spores 
(A),  and  another  one  (B)  from  which 
the  spores  (with  no  cilia)  have  escaped. 


THALLOPHYTES  23 

16.  Sex-reproduction.  —  A  third  method  of  reproduction 
appears  among  the  Algae,  and  it  represents  the  final  stage  in 
the  progress  of  reproduction.  This  method  was  derived  from 
spore-reproduction,  and  some  of  the  Algae  illustrate  this  fact 
completely.  In  Ulothrix  (Fig.  7,  B  and  C),  for  example, 
a  number  of  spores  are  produced  by  a  single  protoplast, 
the  number  of  spores  depending  on  the  number  of  successive 
divisions.  Naturally,  the  more  numerous  the  divisions  are, 
the  smaller  are  the  spores,  so  that  in  Ulothrix  the  number 
and  size  of  the  spores  vary  with  the  number  of  divisions.  It 
is  found  that  the  smaller  spores  produce  feebler  plants,  and 
that  the  divisions  may  become  numerous  enough  to  result 
in  spores  too  small  to  produce  plants  at  all.  Under  these 
circumstances  it  is  observed  that  these  small  and  incapable 
spores  may  pair  with  one  another  and  fuse  to  form  a  single 
cell  (Fig.  7,  C,  d  and  e),  and  that  this  cell  can  produce  a  new 
plant. 

This  act  of  fusing,  by  which  a  reproductive  cell  is  formed, 
is  the  sexual  act,  often  called  fertilization;  the  two  fusing 
cells,  which  are  no  longer  spores  because  they  cannot  pro- 
duce new  plants  alone,  are  sexual  cells,  usually  called  gametes; 
and  the  resulting  cell  with  reproductive  powers  is  an  oospore, 
sometimes  called  the  fertilized  egg.  It  is  evident  that  gametes, 
among  Algae,  are  derived  from  swimming  spores,  and  that  the 
changes  by  which  a  swimming  spore  becomes  a  gamete  are 
the  changes  that  explain  the  origin  of  sex.  It  is  also  evident 
that  the  oospore  is  a  spore,  because  it  produces  a  new  plant, 
but  it  differs  from  the  ordinary  spore  in  the  method  of  its 
origin.  It  is  for  this  reason  that  it  is  distinguished  by  a  pre- 
fix that  means  "  egg,"  implying  that  it  has  been  produced 
by  the  sexual  act.  When  the  word  "spore"  is  used,  the 
ordinary  reproductive  cell,  not  produced  by  the  fusion  of 
two  cells,  is  meant.  Very  often  the  phrases  "  asexual 
spores  "  and  "  sexual  spores  "  are  used  to  distinguish  these 
two  kinds  of  spores,  but  the  latter  phrase  is  misleading,  for 


24  ELEMENTARY   STUDIES   IN   BOTANY 

no  spores  are  "sexual,"  the  only  sexual  cells  being  the 
gametes. 

Spores  and  oospores  are  not  produced  by  Algae  continu- 
ously, for  under  certain  conditions  Algse  may  vegetate,  with- 
out producing  any  spores ;  under  other  conditions  they  may 
produce  spores  freely;  and  under  still  other  conditions 
gametes  appear  and  oospores  are  formed.  In  the  ordinary 
course  of  the  seasons,  the  spores  are  produced  during  the 
growing  season  and  multiply  individuals,  in  fact  they  do 
most  of  the  reproduction.  The  gametes,  on  the  other  hand, 
usually  appear  towards  the  end  of  the  growing  season  for 
the  plant,  and  so  the  formation  of  the  oospores  is  about  the 
last  activity  of  the  plant.  The  spores  germinate  at  once, 
but  the  oospores,  appearing  late  in  the  season,  develop 
heavy  walls,  remain  dormant  through  the  winter,  and  ger- 
minate at  the  beginning  of  the  next  growing  season.  In 
such  plants,  therefore,  the  oospores  are  the  only  structures 
that  remain  alive  through  the  winter.  It  may  be  said, 
therefore,  that  spores  multiply  the  plant,  while  oospores 
protect  it  through  the  winter  and  start  it  again.  In  those 
Algse  in  which  there  is  no  sex,  and  therefore  no  oospores, 
ordinary  vegetative  cells  become  heavy-walled  and  protect 
the  plant  through  the  winter. 

17.  Life-history  formulae.  —  The  life-history  of  a  plant 
means  the  complete  history  of  its  life,  beginning  at  any  point, 
for  example,  the  spore,  and  continuing  until  spores  appear 
again.  It  is  helpful  to  express  the  outlines  of  a  life-history 
by  a  formula,  and  the  following  formulae  illustrate  the  life- 
histories  of  the  Algse  we  have  been  considering.  Vegetative 
multiplication  may  be  indicated  by  P — P — P,  etc.,  in  which 
"  P  "  stands  for  "  plant,"  and  which  indicates  that  one  plant 
produces  another  directly,  without  any  special  cells.  Spore- 
reproduction  may  be  indicated  by  P— a — P — o — P — o,  etc., 
which  indicates  that  the  plant  produces  a  spore  which  pro- 
duces another  plant,  and  so  on.  Sex-reproduction  may  be 


THALLOPHYTES  25 

indicated  by  P=J>o — F~°>o — P,  etc.,  which  indicates 
that  the  plant  produces  two  gametes  which  fuse  to  form  an 
oospore  which  produces  another  plant,  and  so  on.  It  must 
be  remembered  that  in  plants  that  produce  sexual  cells,  all 
three  ways  of  producing  new  plants  are  found,  so  that  a  real 
life-history  formula  for  such  a  plant  would  be  something  as 

follows : 

-P 


This  simply  indicates  the  three  methods  of  producing  new 
plants. 

18.  Differentiation  of  sex.  —  At  the  first  appearance  of 
sex,  the  gametes  are  alike  in  form  and  behavior,  as  in  Ulothrix 
(Fig.  7,  C,  d}.  They  are  approximately  the  same  in  size, 
and  are  both  swimming  cells  with  the  same  arrangement  of 
cilia,  so  that  there  is  no  visible  sex-distinction.  Plants  with 
such  gametes  are  sometimes  called  "  unisexual  plants," 
which  means  plants  having  only  one  sex.  The  phrase  is 
misleading,  for  to  have  sex  at  all,  there  must  be  two  sexes. 
What  the  phrase  really  means  is  that  the  sexes  cannot  be 
distinguished. 

In  other  plants,  however,  the  pairing  gametes  begin  to 
show  differences,  one  being  larger  than  the  other  and  cor- 
respondingly less  active,  until  finally  one  is  relatively  very 
large  and  entirely  passive,  while  the  other  retains  its  small 
size  and  activity.  The  increased  size  of  one  of  the  gametes 
means  an  increased  nutritive  power,  but  this  gain  has  been 
accompanied  by  a  loss  of  swimming  power.  This  develop- 
ment of  obvious  differences  between  the  pairing  gametes 
is  the  differentiation  of  sex,  whereby  the  two  sexes  become 
apparent.  The  large  and  passive  gamete  is  female,  and  is 
called  the  egg;  while  the  small  and  active  gamete  is  male, 
and  is  called  the  sperm.  For  example,  the  illustration  of 
(Edogonium  (Fig.  15,  B)  shows  a  large  egg  (packed  full  of 


26 


ELEMENTARY   STUDIES   IN   BOTANY 


food)  within  a  swollen  cell,  and  small  ciliated  sperms  having 
escaped  from  small  cells  (6) ;  while  the  illustration  of  Fucus 

(Fig.  20)  shows  a  very 
large  egg  surrounded  by 
numerous,  small,  and  very 
active  sperms. 

19.  Differentiation  of 
sex-organs.  -  -  In  such 
Algae  as  Ulothrix  (Fig.  7, 
C),  an  ordinary  vegeta- 
tive cell,  without  any 
change  of  form,  produces 
gametes.  In  other  Algae, 
as  Ectocarpus  (Fig.  16, 
E),  the  cells  that  produce 
gametes  differ  in  form 
from  the  vegetative  cells, 
just  as  the  cells  that 
produce  spores  (A)  differ 
from  them.  Just  as  the 
spore-producing  cells  that 
become  different  from  the 
vegetative  cells  are  called 
sporangia  (§  15,  p.  22),  so 
these  gamete-producing 
cells  that  become  differ- 
ent are  called  gametangia 
("  gamete  -cases")-  A 
gametangium,  therefore, 

Vocc    J.'  ig»   JL&J   uvjuuaaj-ung     u  10,11. unco    jjn_m.u.<Jiii^         ,  j_l~      X      * 

antheridia ;  B,  an  enlarged  view  of  a  branch     IS  a  SCX-Organ,    that    IS,   a 

structure  that   produces 
sex-cells  (gametes). 
When  the  gametes  become  plainly  different,  so  as  to  be 
called  eggs  and  sperms,  the  gametangia  that  produce  them 
become   different   and   receive   distinguishing  names.     The 


FIG.  18.  —  Fucus:    A,  a  chamber  in  the  body 
(see  Fig.  12)  containing  branches  producing 


bearing  antheridia,  in  which  the  sperms  can 
be  seen.  —  After  THURET. 


THALLOPHYTES 


27 


gametangium  that  produces  an  egg  (usually  only  one)  is 
an  oogonium  ("  egg-case  "),  while  the  gametangium  that 
produces  sperms  is  an  antheridium  (a  name  whose  meaning 
explains  nothing). 

There  are  two  distinct  stages  in  the  evolution  of  oogonia 
and  antheridia  that  ought  to  be  recognized.  In  (Edogonium 
(Fig.  15,  B),  for  example,  the  oogonia  and  antheridia  are 
transformed  vegetative 
cells ;  that  is,  cells  which 
do  vegetative  work  may 
later  become  oogonia 
or  antheridia.  But  in 
Vaucheria  (Fig.  21)  and 
Fucus  (Figs.  18,  19),  for 
example,  the  oogonia  and 
antheridia  have  never 
been  a  part  of  the  vege- 
tative body,  but  are  set 
apart  from  the  beginning 
as  special  branches.  In 
these  forms,  therefore, 
the  sex-organs  have  be- 
come completely  differ- 
entiated from  the  rest 
of  the  body. 

20.  Differentiation  of  sex-individuals.  --  There  is  another 
kind  of  sexual  differentiation  that  must  be  recognized.  In 
such  Algae  as  Spirogyra  (Fig.  22),  the  two  gametes  look  alike, 
both  of  them  being  large,  but  one  of  them  remains  passively 
in  its  cell,  while  its  mate  leaves  its  cell,  squeezes  through  a 
connecting  tube,  and  enters  the  other  cell.  The  behavior 
of  the  two  gametes,  therefore,  is  different,  and  it  seems 
proper  to  call  the  passive  one  female  and  the  active  one 
male.  Furthermore,  it  is  very  common  to  find  two  fila- 
ments of  Spirogyra  lying  side  by  side,  all  the  opposing  cells 


FIG.  19.  —  Fucus:    a    cummuer    in    the    body    in 
which  oogonia  are  produced.  —  After  THURET. 


28 


ELEMENTARY   STUDIES   IN   BOTANY 


>Sf 


FIG.  20.  —  Fucus:    A,  the  eight  eggs  discharged  from  the  oogonium;    B   and  C,  egg 
surrounded  by  swarms  of  swimming  sperms.  —  After  STRASBURGER. 

connected  by  tubes,  and  all  of  the  cells  of  one  filament 
empty,  which  means  that  all  of  the  gametes  of  one  filament 
have  passed  over  into  the  cells  of  the  other  filament.  If  the 


FIG.  21.  —  Vaucheria:  A,  part  of  a  filament,  showing  the  special  branches  producing  an 
antheridium  (a,  emptied  in  this  specimen)  and  an  oogonium  (fc)  ;  B,  another  species, 
in  which  a  single  branch  bears  several  oogonia  and  a  terminal  coiled  antheridium. 


THALLOPHYTES 


29 


active  gametes  are  male,  then  the  emptied  filament  is  a  male 
individual,  and  the  receiving  filament  is  a  female  individual. 
In  such  a  case,  there- 
fore, there  is  a  sexual 
differentiation  of  indi- 
viduals, and  in  Spiro- 
gyra  this  occurs  with- 
out any  differentiation 
of  gametes  in  appear- 
ance, and  without  any 
differentiation  of  sex- 
organs. 

After  the  origin  of 
sex,  therefore,  when 
the  formation  of  gam- 
etes is  an  established 
habit,  there  are  three 
kinds  of  differentia- 
tion :  differentiation 
of  gametes,  of  sex- 
organs,  and  of  sex- 
individuals.  These 
different  kinds  of  dif- 
ferentiation may  occur 
singly,  or  any  two  to- 
gether, or  all  three  to- 
gether. When  the  last 
takes  place,  and  we 
find  plants  with  eggs 
and  sperms,  produced 
by  distinctly  set  apart 
oogonia  and  anther- 
idia,  and  these  two 
kinds  of  sex-organs  borne  on  different  individuals,  we  have 
reached  an  extreme  case  of  sexual  differentiation. 


FIG.  22.  —  Spirogyra:  A,  part  of  a  filament,  show- 
ing one  complete  cell,  with  its  central  nucleus 
and  its  characteristic  chloroplast  (the  spiral 
band) ;  B,  cells  of  two  filaments  developing  the 
connecting  tubes ;  C,  the  passage  of  one  pro- 
toplast through  the  tube ;  D,  the  oospore 
formed  by  the  fusing  of  the  two  protoplasts; 
the  emptied  cell  is  therefore  male  and  the  cell 
containing  the  oospore  is  female,  and  if  all  the 
cells  of  each  filament  are  like  the  one  shown, 
the  filaments  (individuals)  are  male  and  female. 


30  ELEMENTARY   STUDIES   IN   BOTANY 

21.  Summary.  —  Algae  represent  the  beginnings  of  the 
plant  kingdom,  and  all  their  structures  are  related  to  water 
as  a  medium. 

The  simplest  body  is  a  single  cell,  but  among  Algae  the 
body  advances  from  the  single  cell,  through  cell-colonies, 
to  the  many-celled  individual,  whose  form  is  prevailingly 
filamentous,  although  other  forms  occur.  Among  the  higher 
Algae,  the  many-celled  body  often  becomes  differentiated 
into  different  regions,  notably  among  the  marine  Algae. 

The  simplest  form  of  reproduction  is  vegetative  multipli- 
cation. In  addition  to  this,  Algae  developed  reproduction 
by  means  of  spores,  which  in  most  cases  are  swimming  cells. 
Among  the  Algae  there  appears  also  sexual  reproduction,  at 
first  the  gametes  seeming  to  be  alike,  then  differentiating 
into  sperms  and  eggs.  The  two  kinds  of  gametes  at  first 
are  produced  by  ordinary  vegetative  cells,  but  later  special 
cells  produce  them,  which  are  therefore  sex-organs. 


CHAPTER   III 
FOOD  MANUFACTURE 

22.  Peculiar  work  of  green  plants. — The  Algae  differ  from 
other  Thallophytes  in  containing  chlorophyll  (§  10,  p.  10). 
The  presence  of  this  pigment  is  so  common  among  plants 
that  vegetation  is  thought  of  as  being  green,  but  very  many 
plants  are  not  green.  Even  those  that  contain  chlorophyll 
are  not  always  green  in  appearance,  for  this  pigment  may  be 
obscured  by  others.  For  example,  there  are  four  groups 
of  Algae  that  are  distinguished  by  their  color,  although  all  of 
them  contain  chlorophyll.  The  two  conspicuous  groups  of 
fresh-water  Algae  are  called  "  Blue-green  Algae "  (Cyano- 
phycece)  and  "Green  Algae"  (Chlorophycece)  because  in  the 
former  a  blue  pigment  is  associated  with  the  green,  giving 
the  plant  a  bluish  green  tint,  and,  in  the  latter,  chlorophyll 
is  the  only  pigment.  The  two  conspicuous  groups  of  marine 
Algae  are  called  "  Brown  Algae  "  (Phceophycece)  and  "  Red 
Algae  "  (Rhodophycece)  because  in  the  former  certain  brown 
and  yellow  pigments  are  associated  with  the  green  and  often 
mask  it  completely,  and  in  the  latter  a  red  pigment  obscures 
the  green. 

The  presence  of  chlorophyll  in  the  Algae  gives  them  a 
peculiar  power  among  Thallophytes,  a  power  that  all  green 
plants  possess.  It  is  the  power  of  manufacturing  food. 
It  is  perhaps  impossible  to  define  exactly  what  is  meant  by 
food,  but  in  general  it  means  material  that  protoplasm  can 
use  in  building  up  its  body.  All  living  things  must  use  food, 
but  only  green  plants  can  make  it.  This  process,  therefore, 
is  one  of  the  very  greatest  importance,  for  the  existence  of 
all  plants  and  animals  depends  upon  it. 

31 


32  ELEMENTARY   STUDIES   IN   BOTANY 

Substances  are  said  to  be  either  organic  or  inorganic.  An 
organic  substance  is  one  that  is  made  by  a  living  body ;  an 
inorganic  substance  is  one  that  is  usually  made  quite  inde- 
pendently of  a  living  body,  as  air,  water,  compounds  in  the 
soil,  rock  material,  etc.  The  manufacture  of  food  consists 
in  taking  these  inorganic  substances  and  making  from  them 
organic  substances.  It  is  this  that  green  plants  are  able 
to  do,  and  they  manufacture  food  not  only  for  their  own 
use,  but  also  for  the  use  of  plants  that  are  not  green  as  well  as 
for  the  use  of  all  animals.  The  food  used  by  plants  does  not 
differ  from  that  used  by  animals ;  the  difference  is  that  green 
plants  have  the  added  power  of  manufacturing  food.  A 
miller  uses  flour  for  his  bread,  just  as  every  one  else  does, 
but  he  differs  from  others  in  also  being  equipped  to  manu- 
facture his  flour. 

There  are  several  general  kinds  of  food,  but  the  peculiar 
work  of  green  plants  has  to  do  with  only  one  of  them,  the 
kind  called  carbohydrates.  If  this  name  does  not  happen 
to  suggest  any  kind  of  food,  such  common  carbohydrates  as 
sugar  and  starch  will  make  the  kind  clear  to  every  one. 
The  importance  of  the  manufacture  of  carbohydrates,  which 
is  the  peculiar  work  of  green  plants,  is  recognized  when  it  is 
known  that  in  the  manufacture  of  the  other  foods  carbohy- 
drates must  be  used.  This  means  that  although  carbohydrates 
are  not  the  only  kind  of  food,  they  are  the  necessary  start  for 
all  other  kinds. 

23.  The  raw  material.  —  It  is  important  to  know  the 
inorganic  substances  a  green  plant  uses  in  the  manufacture 
of  carbohydrates.  They  cannot  be  rare  substances,  or 
vegetation  would  not  be  so  common.  They  are  water  and 
carbon  dioxide.  The  former  needs  no  explanation;  the 
latter  is  often  called  "  carbonic  acid  gas,"  and  is  the  so- 
called  "  impure  "  gas  that  accumulates  in  badly  ventilated 
rooms.  Carbon  dioxide  is  everywhere  in  the  air,  in  very 
small  proportion  (about  three  parts  in  10,000),  and  is  more 


FOOD   MANUFACTURE  33 

abundant  in  quiet  waters,  in  which  it  is  dissolved  not  only 
from  the  air,  but  also  from  the  breathing  and  decay  of  the 
innumerable  plants  and  animals  that  live  in  water.  The 
Algae  naturally  obtain  it  from  the  water  in  which  they  are 
living;  while  plants  living  on  land  obtain  it  from  the  air, 
chiefly  through  their  leaves.  The  Algae  need  no  special 
equipment  for  obtaining  water,  for  their  bodies  are  exposed 
to  it  and  it  enters  all  the  cells  freely ;  but  in  the  case  of  land 
plants,  the  special  equipment  is  usually  a  root  system  into 
which  water  enters  from  the  soil. 

An  important  feature  of  these  two  substances  that  the 
green  plant  uses  in  carbohydrate  manufacture,  is  that  they 
are  what  are  called  "  ultimate  wastes  "  when  food  is  being 
used.  This  phrase  means  that  in  our  bodies,  for  example, 
carbon  dioxide  and  water  are  disposed  of  because  the  body 
does  not  use  them,  and  it  does  not  use  them  because  they 
are  so  difficult  to  break  up  as  preliminary  to  forming  new 
combinations.  The  ultimate  wastes  of  living  bodies,  there- 
fore, can  be  used  by  green  plants  as  the  raw  materials  for 
the  manufacture  of  food.  From  food  to  waste  is  the  work 
going  on  in  all  living  bodies ;  from  waste  to  food  is  the  added 
work  going  on  in  all  green  plants. 

24.  The  agent.  —  The  active  agent  in  the  manufacture 
of  carbohydrates  is  the  (ihloroplast  (§  10,  p.  10,  and  Fig.  1). 
As  the  name  implies,  a  chloroplast  consists  of  two  conspicu- 
ous substances:  (1)  the  living  protoplasm  (plastid),  and 
(2)  the  green  pigment  (chlorophyll).  They  can  be  separated 
from  one  another  by  soaking  green  parts  (as  leaves)  in  alcohol, 
which  extracts  the  chlorophyll  and  leaves  the  plastids  color- 
less. Just  what  each  of  these  substances  does  in  the  manu- 
facture of  carbohydrates  is  not  known  with  certainty,  but 
it  is  certain  that  both  are  necessary.  The  plastid  is  alive 
and  the  chlorophyll  is  not,  but  since  the  manufacture  of 
carbohydrates  is  a  chemical  process,  the  chlorophyll  may  be 
the  cause  of  some  of  the  changes.  In  fact,  a  chloroplast 


34  ELEMENTARY    STUDIES   IN    BOTANY 

may  be  thought  of  as  a  chemical  laboratory,  which  uses  cer- 
tain substances  in  the  manufacture  of  others. 

25.  The  energy.  —  Those  who  have  studied  physics  are 
aware  that  energy,  the  power  for  work,  is  as  real  a  thing  as 
the  material  to  work  with.     It  is  important,  therefore,  to 
discover  the  source  of  the  energy  used  in  the  manufacture 
of    carbohydrates.     The    chloroplast    obtains    this    energy 
from  sunlight,  and  it  is  known  that  chlorophyll  is  able  to 
absorb  energy  from  light.     It  is  evident  that  this  absorbed 
energy,  in  some  form,  is  used  in  the  chloroplast.     It  follows 
that  carbohydrates  can  be  produced  by  green  plants  only 
when  exposed  to  the  light,  and  that  at  night  the  process  is 
suspended.     In  fact,  many  green  plants  may  live  through 
the  winter,  in  the  form  of  bulbs,  tubers,  etc.,  without  any 
opportunity   to    manufacture    food.     It   must    be    evident, 
therefore,  that  a  process  which  is  suspended  for  a  consider- 
able period  during  every  twenty-four  hours,  and  that  may 
be  suspended  for  months,  is  not  a  process  of  living,  which 
involves  the  use  of  food,  for  living  must  go  on  continuously. 
It  is  simply  a  manufacture,  which  has  nothing  to  do  with 
the  process  of  living  except  that  it  provides  the  material 
that  is  used  in  the  process  of  living.     It  holds  the  same 
relation  to  the  process  of  living  that  the  baker  holds  to  us 
in  manufacturing  bread. 

It  is  important  to  observe  that  light  is  essential  not  only 
to  the  manufacture  of  carbohydrates,  but  also  to  the  manu- 
facture of  chlorophyll  itself.  If  light  is  withdrawn  from  a 
green  plant  for  a  considerable  period,  the  plant  loses  its  green 
color,  as  when  a  board  lies  for  some  time  upon  the  grass, 
or  when  earth  is  heaped  about  celery  to  blanch  it.  When 
potatoes  "  sprout  "  in  a  dark  cellar,  the  young  shoots  are 
pallid,  but  if  exposed  to  light  they  become  green. 

26.  The  process.  —  The  manufacture  of    carbohydrates 
by  green  plants  has  received  a  name  suggestive  of  the  process. 
It  is  called  photosynthesis,  which  means  putting  together  in  the 


FOOD   MANUFACTURE  35 

presence  of  light.  The  word  "  photograph"  shows  the  same 
use  of  the  word  light,  and  the  process  of  "  photography  " 
shows  the  same  activity  of  light  in  causing  chemical  changes. 
The  first  step  in  the  process  seems  to  be  the  "  breaking  up  " 
of  the  water  and  carbon  dioxide  into  their  constituent  ele- 
ments. Those  who  have  studied  chemistry  know  that  water 
is  a  combination  of  the  two  elements  hydrogen  and  oxygen, 
both  of  them  gases,  in  the  proportion  of  two  parts  of  hydrogen 
to  one  part  of  oxygen,  so  that  the  formula  for  water  is  H2O. 
Carbon  dioxide  is  also  a  combination  of  two  elements,  carbon 
and  oxygen,  and  its  formula  is  C02.  To  break  up  these  two 
substances,  so  that  the  water  splits  into  the  two  gases  that 
compose  it  and  the  carbon  dioxide  splits  into  the  gas  and  the 
solid  that  compose  it,  is  a  process  that  requires  a  great  dis- 
play of  energy,  in  the  form  of  heat,  electricity,  etc.,  when 
done  in  the  laboratory ;  but  it  is  accomplished  by  the  green 
plant  without  any  unusual  display  of  energy. 

Following  the  breaking  up  (analysis)  of  the  raw  materials, 
the  elements  are  put  together  in  new  combinations,  the 
"  putting  together  "  being  the  "  synthesis  "  referred  to  in 
the -name  photosynthesis.  It  must  not  be  supposed  that  a 
carbohydrate  is  the  result  of  the  first  synthesis,  for  it  is 
reached  only  after  a  series  of  chemical  changes. 

27.  The  product.  —  The  final  product  of  photosynthesis 
is  reached  when  a  carbohydrate  is  formed.  If  the  raw  ma- 
terials and  the  final  product  are  compared,  certain  important 
facts  become  evident.  The  simplest  method  of  comparison 
is  to  use  the  following  equation  :  C02  +  H20  =  QHaO  +  O2. 
The  first  side  of  the  equation  represents  the  raw  materials, 
and  the  other  side  represents  the  carbohydrate  product  and 
the  oxygen  left  over.  CH20  is  not  the  formula  for  a  car- 
bohydrate, but  it  may  be  called  the  carbohydrate  unit,  which 
by  using  various  multiples  becomes  the  formula  of  various 
carbohydrates.  For  example,  a  simple  carbohydrate  is 
C6Hi2O6,  in  which  6  is  the  multiple,  and  most  other  carbo- 


36  ELEMENTARY    STUDIES   IN    BOTANY 

hydrates  are  multiples  of  6.  In  examining  the  second  hall 
of  the  equation,  it  becomes  evident  (1)  that  the  carbohydrate 
contains  hydrogen  and  oxygen  in  the  same  proportion  as  in 
water,  a  fact  which  gives  name  to  the  compound  ("  carbohy- 
drate "  means  carbon  and  water) ;  and  (2)  that  oxygen  is 
freed  as  a  waste  product  (or  by-product)  in  the  same  propor- 
tion as  it  exists  in  carbon  dioxide.  The  total  result  is  to  get 
the  carbon  out  of  the  carbon  dioxide  and  combine  it  with 
water,  and  therefore  the  process  is  often  called  the  "  fixation  " 
of  carbon.  Hydrogen  and  oxygen  are  gases,  so  that  carbon 
is  the  only  solid  that  enters  into  the  fabric  of  the  plant,  and 
this  solid  is  obtained  from  a  gas  that  exists  in  the  air. 

The  carbohydrates  thus  formed  in  the  plant  are  usually 
starches  or  sugars,  and  they  are  freely  transformed  into  one 
another.  It  is  often  stated  that  green  plants  form  starch, 
but  the  fact  is  that  starch  is  only  the  visible  form  of  the  carbo- 
hydrate. It  is  visible  because  it  does  not  dissolve  in  the  cell 
sap,  while  sugar  is  invisible  because  it  does  dissolve.  When 
more  carbohydrate  is  manufactured  than  is  being  used,  it 
becomes  stored  up  in  the  form  of  starch,  and  therefore  starch 
is  spoken  of  as  the  storage  form  of  a  carbohydrate.  On  the 
other  hand,  when  the  carbohydrate  is  being  used  and  is 
being  carried  around  through  the  plant,  it  is  in  the  form  of 
sugar,  for  a  substance  must  be  in  solution  to  be  carried  about, 
and  therefore  sugar  is  spoken  of  as  the  transfer  form  of  a 
carbohydrate. 

28.  The  by-product.  —  It  has  been  noted  that  during 
photosynthesis  oxygen  is  given  off  as  a  by-product.  Nothing 
more  than  a  statement  of  this  fact  would  be  needed  if  it  were 
not  connected  with  a  persistent  misconception  in  reference 
to  photosynthesis.  When  it  was  first  observed  that  green 
plants  take  in  carbon  dioxide  and  give  out  oxygen,  it  was 
natural  to  suppose  that  this  gas  exchange  represented  the 
respiration  of  plants.  Since  the  gas  exchange  in  the  respira- 
tion of  animals  is  just  the  reverse  (taking  in  oxygen  and  giving 


FOOD   MANUFACTURE  37 

out  carbon  dioxide),  the  opinion  became  current  that  plants 
and  animals  differ  in  their  "  breathing."  As  a  corollary  to 
this  opinion,  it  was  pointed  out  that  animals  and  plants 
supplement  each  other  in  this  process,  each  taking  in  what 
the  other  gives  off,  and  each  living  on  what  the  other  rejects. 
Since  this  impression  is  still  current,  its  correction  must  be 
emphasized.  It  is  clear  that  photosynthesis  has  nothing  to 
do  with  respiration,  for  respiration  is  associated  with  what 
may  be  called  the  act  of  living,  and  therefore  is  carried  on  by 
every  living  thing.  If  respiration  stops,  the  plant  or  animal 
body  is  dead;  in  fact,  we  use  respiration  as  an  evidence  of 
life.  Therefore  plants  and  animals  "  breathe  "  alike,  both 
taking  in  oxygen  and  giving  out  carbon  dioxide ;  but  green 
plants  can  carry  on  the  process  of  photosynthesis  also,  in 
connection  with  which  it  takes  in  carbon  dioxide  and  gives 
out  oxygen.  The  confusion  arose  from  the  fact  that  during 
the  day,  when  photosynthesis  is  going  on,  the  amount  of  the 
gas  exchange  involved  in  the  manufacture  of  carbohydrates  is 
so  much  greater  than  the  amount  involved  in  respiration 
that  the  latter  was  not  noticed ;  but  if  the  observation  had 
extended  into  the  night,  it  would  have  been  discovered  that 
only  the  gas  exchange  of  respiration  was  being  carried  on. 

It  may  be  useful  to  contrast  photosynthesis  and  respira- 
tion sharply  as  follows :  photosynthesis  occurs  only  in  green 
cells,  requires  light,  uses  carbon  dioxide,  liberates  oxygen, 
makes  organic  material,  and  accumulates  energy;  while 
respiration  occurs  in  every  living  cell,  does  not  require  light, 
uses  oxygen,  liberates  carbon  dioxide,  uses  organic  material, 
and  uses  energy. 

29.  Manufacture  of  proteins.  —  Carbohydrates  are  by 
no  means  the  only  foods,  and  'therefore  photosynthesis  is 
not  the  only  process  of  food  manufacture.  Another  conspicu- 
ous group  of  foods  is  the  proteins,  which  may  be  regarded 
as  foods  in  the  most  advanced  stage,  since  the  living  proto- 
plasm is  largely  composed  of  proteins.  Carbohydrates, 
4 


38  ELEMENTARY    STUDIES   IN   BOTANY 

therefore,  may  be  thought  of  as  the  first  stage  of  food,  and 
proteins  as  the  last  stage. 

The  constitution  of  proteins  is  not  known,  so  that  their 
manufacture  is  not  understood.  It  is  known  that  neither 
light  nor  chlorophyll  is  required,  for  the  process  goes  on  in 
living  cells  removed  from  light,  and  in  plants  containing  no 
chlorophyll.  It  is  known,  however,  that  carbohydrates  are 
used,  and  that  to  the  carbon,  hydrogen,  and  oxygen  supplied 
by  them,  the  elements  nitrogen,  sulphur,  and  often  phos- 
phorus are  added.  It  is  important  to  know  the  sources  of 
these  new  elements  that  enter  into  food  manufacture.  They 
are  not  used  by  the  plant  as  free  elements,  but  are  obtained 
from  their  combinations  in  what  are  called  salts.  For  ex- 
ample, salts  containing  these  elements  occur  in  all  soils  upon 
which  plants  can  grow,  and  these  same  salts  are  dissolved 
in  the  water  in  which  AlgaB  grow.  In  land  plants,  they  enter 
through  the  roots,  while  in  Algae  they  enter  wherever  the 
plant  is  exposed  to  water. 

30.  Assimilation.  —  While   the    processes   of   food-manu- 
facture are  being  considered,  it  will  be  helpful  to  define  the 
use  of  food.     There  is  an  intermediate  process  called  digestion, 
which  simply  means  the  conversion  of  foods  into  transfer 
forms,  usually  soluble  forms.     For  example,  digestion  trans- 
forms  insoluble   starch   into   soluble   sugar.     It  is   evident, 
furthermore,  that  only  those  foods  need  to  be  digested  which 
are  not  in  transfer  form. 

The  process  by  which  foods  are  used  in  the  manufacture 
of  protoplasm  is  called  assimilation.  Protoplasm  is  the 
living  body  and  it  uses  food  to  construct  more  protoplasm. 

31.  Respiration.  —  Everything  about  the  plant  is  a  pro- 
duct of  protoplasm,  and  in  doing  the  great  variety  of  work 
that  goes  on  in  a  living  body  the  protoplasm  "  breaks  down," 
using  itself  up  continually  in  the  manufacture  of  products. 
Of  course  this  explains  why  it  must  be  assimilating  all  the 
time,  so  that  its  body  may  be  continually  built  up.     This 


FOOD   MANUFACTURE  39 

process  of  breaking  down  the  protoplasmic  body  is  respira- 
tion, and  one  of  the  superficial  indications  that  respiration 
is  going  on  is  that  oxygen  is  taken  in  and  carbon  dioxide  is 
given  off.  This  gas  exchange,  therefore,  is  not  respiration, 
but  is  merely  the  external  evidence  that  the  process  is  going 
on. 

32.  Summary.  —  The  peculiar  work  of  green  plants  is  to 
manufacture  carbohydrates.  The  raw  materials  used  are 
carbon  dioxide  and  water,  which  the  chloroplasts,  with  energy 
obtained  from  sunlight,  use  in  the  manufacture,  a  certain 
amount  of  oxygen  being  given  off  as  a  by-product.  The  car- 
bohydrates thus  manufactured  are  the  basis  of  other  foods  (as 
proteins).  Water  and  carbon  dioxide,  therefore,  are  not  foods, 
but  materials  from  which  foods  are  manufactured.  The  food 
of  all  plants  and  animals  is  the  same,  and  when  used  it  is 
digested  (if  necessary)  and  assimilated  (built  up  into  proto- 
plasm) ;  and  the  evidence  that  the  living  protoplasm  is 
working  is  that  respiration  is  going  on,  an  external  indication 
of  which  is  the  entrance  of  oxygen  and  the  escape  of  carbon 
dioxide.  All  plants  and  animals,  therefore,  use  the  same 
food  and  "  breathe  "  in  the  same  way,  but  only  green  plants 
can  manufacture  food  from  material  that  is  not  food. 


CHAPTER   IV 
THALLOPHYTES  —  2.   FUNGI 

DEPENDENT  PLANTS 

33.  The  dependent  habit.  —  The  Algae    are  said    to    be 
independent  plants  because  they  can  manufacture  carbo- 
hydrates from  inorganic  material.     This  means  that  they  do 
not  depend  upon  any  other  plants  or  animals  for  their  food 
supply,  and  therefore  could  live  and  work  if  they  were  the 
only  organisms  in  existence.     The  Fungi,  on  the  other  hand, 
are  those  Thallophytes  that  have  no  chlorophyll,  and  there- 
fore cannot  manufacture  carbohydrates.     This  means  that 
they  must  depend  upon  other  plants  and  upon  animals  for 
their  food  supply,  and  that  they  could  not  exist  in  the  ab- 
sence of  green  plants. 

It  must  not  be  supposed  that  Fungi  are  the  only  dependent 
plants,  for  even  among  seed-plants  there  are  those  without 
chlorophyll,  as  Indian  pipe  and  a  number  of  orchids,  that  are 
compelled  to  obtain  their  food  from  other  organisms.  But 
the  Fungi  represent  by  far  the  greatest  assemblage  of  de- 
pendent plants. 

34.  Parasites  and  saprophytes.  —  If  Fungi  must   obtain 
their  food  from  other  organisms,  it  should  be  recognized  that 
there  are  two  general  conditions  in  which  this  food  occurs. 
It  is  either  a  part  of  the  living  body  of  a  plant  or  animal, 
or  material  that  has  been  produced  by  a  living  body  and  is 
no  longer  connected  with  it.     For  example,  when  the  rust 
fungus  attacks  wheat,  it  is  obtaining  food  from  living  plants ; 

40 


THALLOPHYTES  41 

but  when  a  mold  fungus  attacks  bread,  it  is  obtaining  food 
from  material  produced  by  living  plants,  but  no  longer  con- 
nected with  them.  Fungi  (like  the  rust)  that  attack  living 
bodies  are  called  parasites;  while  those  (like  the  mold)  that 
attack  organic  material  no  longer  connected  with  a  living 
body  are  called  saprophytes. 

It  must  not  be  thought  that  parasite  and  saprophyte  are 
terms  of  classification.  They  refer  only  to  two  sources  of 
food  supply,  and  there  are  many  Fungi  able  to  obtain  food 
from  both  sources.  Naturally,  some  Fungi  are  usually  para- 
sites, and  some  are  usually  saprophytes,  but  they  all  obtain 
food  from  any  available  source.  In  fact,  many  so-called 
parasites  do  not  attack  the  living  cells  of  plants,  but  live 
in  the  vessels  carrying  water  ("  sap  ")  and  thus  choke  them. 
It  is  convenient,  however,  in  a  general  way,  to  distinguish 
between  the  parasitic  habit  and  the  saprophytic  habit,  for 
while  the  former  often  brings  trouble  to  living  plants  and 
animals,  the  latter  does  not. 

The  plant  or  animal  attacked  by  a  parasite  is  called  its 
host,  and  when  the  attack  interferes  with  the  vigor  of  the 
host,  the  latter  is  said  to  be  diseased.  It  is  important  to 
understand  what  is  meant  by  disease,  for  there  is  often  con- 
fusion in  using  the  word.  For  example,  rust  is  often  spoken 
of  as  a  disease  of  wheat  and  other  cereals,  when,  in  fact,  rust 
is  the  parasitic  fungus  that  induces  the  disease. 

The  range  of  attack  by  parasites  is  extremely  variable. 
For  example,  some  parasites  attack  many  kinds  of  plants; 
others  attack  only  a  certain  family  of  plants ;  others  attack 
still  smaller  groups;  and  still  others  attack  only  one  kind 
(species)  of  plant,  and  often  can  select  that  species  with  more 
certainty  than  does  the  botanist.  Parasites  differ  also  in  the 
amount  of  the  host  attacked.  For  example,  some  attack 
the  whole  plant ;  others  attack  only  certain  general  regions 
(as  shoots  or  flowers) ;  while  still  others  may  be  restricted 
to  a  single  kind  of  organ. 


42  ELEMENTARY    STUDIES    IN   BOTANY 

35.  Economic  importance.  —  It  was  said  of  Algae  that  they 
are  of  little  or  no  economic  importance,  but  of  very  great 
scientific  importance  in  the  history  of  the  plant  kingdom. 
This  statement  may  be  reversed  for  Fungi.     They  are  of 
little  scientific  importance  in  the  history  of  the  plant  king- 
dom, but  of  very  great  economic  importance.     In  denning 
parasites,  it  was  stated  that  they  induce  disease,  and  when  it 
is  realized  that  these  plant  parasites  are  responsible  for  many 
diseases  that  ravage  crops,  domesticated  animals,  and  the 
human  population,   it  would   be   hard  to   exaggerate  their 
economic  importance.     It  is  on  account  of  this  importance 
that  the  parasitic  fungi  have  received  so  much  attention,  for 
they  represent  an  enemy  against  which  men  must  always 
be  on  guard. 

On  the  other  hand,  the  work  of  the  saprophytes  is  often 
beneficial.  They  may  be  regarded  as  natural  scavengers, 
decomposing  dead  bodies  and  organic  waste  into  their  con- 
stituent elements  or  inorganic  compounds.  Advantage  is 
taken  of  this  process  in  various  manufactures,  such  as  the 
manufacture  of  alcohol  from  sugars,  the  fermentation  of  fruit 
juices  in  the  manufacture  of  wines,  the  "  raising  "  of  bread 
dough  by  yeasts,  etc. 

36.  Origin  of  Fungi.  —  It  is  a  common  belief  that  Fungi 
are  Alga3  that  have   lost  the   power  of  food-manufacture. 
Some  Algae  and  Fungi  resemble  one  another  so  closely  in 
structure  that  this  belief  seems  reasonable ;   but  most  Fungi 
differ  so  much  from  all  known  Algae  that  such  a  connection 
does  not  seem  convincing.     It  is  easy  to  understand  how 
Algae  might  lose  the  power  of  food-manufacture  if  exposed 
to  an  available  food  supply.     For  example,   certain  Algae 
inhabit  cavities  in  the  bodies  of  green  plants,  and  the  food 
manufactured  by  these  plants  might  be  available  for  the  Algae, 
which  might  thus  gradually  become  dependent. 

Perhaps  the  best  reason  for  believing  that  Fungi  are 
degenerate  Algae  is  that  probably  the  two  groups  existed 


THALLOPHYTES 


43 


together  before  any  other  plants  appeared,  and  that  under 
such  conditions  Fungi  could  not  appear  until  after  Algae 


FIG.  23.  —  Bacteria  of  various  kinds,  mostly  ciliated ;    F  is  the  bacterium  of  typhoid 
fever,  and  H  that  of  cholera.  —  After  ENOLER  and  PRANTL. 

had  started  the  business  of  food-manufacture.     However,  we 
know  nothing  of  the  history  of  plants  before  the  Algae  and 


44 


ELEMENTARY   STUDIES   IN   BOTANY 


Fungi  that  we  see,  so  that  any  statement  as  to  the  relation- 
ship of  these  two  groups  is  at  best  a  hypothesis  that  may  or 
may  not  be  true. 

37.  Bacteria.  —  One  of  the  prominent  groups  of  Fungi  is 
called  bacteria,  a  name  that  has  become  very  familiar  in 
connection  with  the  study  of  human  diseases,  sanitation, 
etc.  Once  bacteria  were  spoken  of  as  "  germs  of  disease," 
and  were  often  thought  of  as  minute  animals.  It  is  impos- 
sible to  overestimate  their  importance  to  man  from  the  stand- 


Hit 


FIG.  24.  —  Some  bacteria  of  fermentation  and  disease:   bacteria  of   souring  milk  (A), 
of  vinegar  (£),  of  diphtheria  (C),  of  tetanus  or  lockjaw  (£>).  —  After  FISCHER. 

point  of  his  personal  interest.  It  is  this  fact  that  has  stimu- 
lated the  study  of  bacteria  to  such  an  extent  that  it  has 
become  a  special  subject  known  as  bacteriology. 

Bacteria  include  the  smallest  known  plants,  some  of  them 
being  visible  only  under  the  highest  powers  of  the  micro- 
scope, and  doubtless  there  are  some  that  are  even  smaller, 
and  have  remained  invisible.  They  are  single  cells  (spheri- 
cal, oblong,  rod-like,  or  curved),  and  occur  either  singly  or 
held  together  usually  in  filaments  (Figs.  23  and  24).  Often 
they  have  cilia  and  swim  freely,  and  this  fact  probably  first 
suggested  that  they  are  minute  animals.  They  occur  every- 
where, in  all  waters,  in  air,  in  soil,  in  all  plants  and  animals 
(living  or  dead).  A  striking  feature  is  their  power  of  en- 
during some  conditions  that  would  destroy  other  plants,  as 
extremes  of  temperature,  great  dryness,  etc.  Their  only 


THALLOPHYTES 


45 


method  of  reproduction  is  by  means  of  vegetative  multi- 
plication, but  this  multiplication  proceeds  with  such  remark- 
able rapidity  that  a  single  cell  may  give  rise  to  millions  of 
cells  in  twenty-four  hours.  Some  of  the  important  work 
done  by  bacteria  may  be  outlined  as  follows. 

Some  bacteria  attack  dead  bodies  of  plants  and  animals, 
or  organic  material  produced  by  plants  and  animals   result- 


FIG.  25.  —  Diagram  of  Mucor,  showing  the  profusely  branching  mycelium  and  three 
sporophores,  one  of  which  bears  a  sporangium.  —  After  ZOPF. 

ing  in  what  is  called  putrefaction  or  fermentation  (Fig.  24, 
A  and  B).  All  of  this  work  is  of  large  service,  but  special  use 
is  made  of  certain  of  the  fermentations,  as  already  mentioned. 
Other  bacteria  attack  living  plants  and  animals,  producing 
various  diseases,  which  are  regarded  as  important  so  far  as 
they  affect  our  cultivated  plants,  our  domesticated  animals, 
and  ourselves.  Many  of  the  common  and  most  dangerous 
diseases  of  the  human  race,  such  as  typhoid  fever  (Fig.  23,  F), 


46 


ELEMENTARY   STUDIES   IN   BOTANY 


diphtheria  '(Fig.  24,  C),  tuberculosis,  and  pneumonia,  as 
well  as  some  very  destructive  plant  diseases,  are  caused  by 
these  bacteria. 

Other  bacteria  live  in  the  soil,  and  are  of  enormous  im- 
portance in  changing  the  materials  of  the  soil  and  in  adding 
new  material  to  the  soil,  making  it  possible  for  other  plants 
to  use  the  soil.  The  great  importance  of  these  bacteria  to 
agriculture  is  coming  to  be  recognized. 

38.  True  Fungi.  —  The  bodies  of  true  Fungi  consist  of 
filaments,  which  may  be  interwoven  more  or  less  compactly. 
For  example,  the  weav- 
ing may  be  so  loose 
that  the  body  is  as 
delicate  as  a  spider 
web,  or  it  may  be  so 
close  that  the  body  is 
almost  as  compact 
as  felt.  This  filamen- 
tous body  is  called  a 
mycelium  (Fig.  25). 

Molds.  —  The  ordi- 
nary mold  that  ap- 
pears as  a  white  furry 
growth  on  stale  bread 
(when  kept  moist  and 
warm)  may  be  taken 
as  an  illustration  (Fig.  25).  The  mycelium  must  be 
related  to  its  food  supply,  and  therefore  it  is  observed 
spreading  over  the  surface  of  the  bread,  evidently  being 
a  true  saprophyte.  Branches  from  the  mycelium  penetrate 
the  bread,  and  into  them  the  nutrient  solution  from  the 
bread  passes.  These  branches  that  receive  the  food  supply 
are  called  hausloria  ("  suckers  "),  and  of  course  are  a  very 
essential  part  of  the  vegetative  body. 

Under  suitable  conditions,  the  prostrate  mycelium  also 


FIG.  26.  —  Section  of  a 
sporangium  of  Mucor 
developing,  and  show- 
ing how  the  partition 
wall  is  pushed  up  into 
the  cavity  of  the 
sporangium. 


FIG.  27.  —  Section  of  a 
mature  sporangium 
of  Mucor,  showing 
the  spores. 


THALLOPHYTES 


47 


u;ives  rise  to  erect  branches,  whose  tips  become  sporangia 
that  produce  vast  numbers  of  spores  that  are  scattered  by 
currents  of  air  (Figs.  26  and  27).  These  spore-bearing 
branches  are  well  called  sporophores  ("  spore-bearers  "). 

Under  other  conditions,  two  neighboring  -mycelia  form 
special  branches  that  come  together  in  pairs,  tip  to  tip  (Fig. 
28).  Each  tip  is  cut  off  frpm  the  rest  of  the  body  by  a  wall, 
and  the  protoplasts  of  the  two  cells  thus  formed  fuse,  and  a 
heavy-walled  oospore  is  the  result.  This  means  thajt  each 
tip-cell  is  a  gametangium,  and 
that  the  fusing  protoplasts  are 
gametes.  The  gametes  and  the 
gametangia  usually  look  alike 
(Fig.  28,  B)  and  behave  alike, 
but  it  is  found  that  the  mycelia 
are  sexually  different.  In  some 
cases  the  gametangia  differ  in 
size  (Fig.  28,  C),  so  that  a  sexual 
difference  is  evident.  Although 
one  mycelium  looks  very  much 
like  another,  the  formation  of 
oospores  will  not  take  place 
unless  sexually  different  mycelia 
are  brought  together.  For  this 
reason  the  mycelium  of  molds 
may  be  grown  indefinitely  with- 
out producing  oospores. 

The  four  things  to  observe, 
therefore,  in  the  study  of  a  true 

fungus,  are  the  mycelium,  the  haustoria,  the  sporophores, 
and  the  sexual  apparatus.  A  comparison  of  the  mold  with 
some  other  Fungi  will  illustrate  how  these  four  things  vary. 

Downy  mildews.  —  There  is  a  group  of  Fungi  called  the 
"  downy  mildews/'  which  attack  a  great  many  plants,  pro- 
ducing such  diseases  as  potato  rot,  grape  mildew,  and  com- 


Fio.  28.  —  Sexual  reproduction  of 
Mucor:  A,  the  sexual  branches  in 
contact ;  B,  the  two  sex-organs 
(gametangia)  cut  off  by  walls ;  C, 
the  two  pairing  sexual  branches 
and  their  gametangia  unequal  in 
size ;  D,  the  oospore  formed  by 
the  fusion  of  the  protoplasts  of 
the  two  gametangia. 


48 


ELEMENTARY   STUDIES   IN   BOTANY 


mon  diseases  on  many  vegetables.  In  this  group  the  my- 
celium lives  upon  a  plant  host  and  is  a  true  parasite.  It 
does  not  spread  upon  the  surface  of  the  host,  but  penetrates 
within  it,  crowding  its  way  between  the  living  cells  of  the  host 
(Fig.  29) .  Thus  it  is  not  only  a  parasite,  but  also  an  internal 
parasite.  From  its  position  against 
the  living  cells  of  the  host,  the  myce- 
lium sends  its  haustoria  through  the 
cell-walls  (Fig.  29),  and  into  these 
haustoria  the  cell-sap  of  the  proto- 
plast enters,  so  that  the  protoplast 
is  dried  out  and  dies.  When  a  myce- 
lium is  living  in  this  way  in  the  interior 
of  a  leaf,  as  a  grape  leaf,  the  drying 
out  and  killing  of  the  leaf-cells  by  the 
haustoria  is  shown  by  the  discolored 
and  finally  brownish  spots  that  ap- 
pear on  the  leaves. 


FIG.  29.  —  Downy  mildew :  branch  of  mycelium  in 
contact  with  two  cells  of  a  host  plant,  and  send- 
ing into  them  branching  haustoria.  —  After  DE 
BARY. 


FIG.  30.  —  Downy  mil- 
dew: sporophores 
emerging  through  the 
"breathing  pores" 
of  a  leaf,  branching, 
and  bearing  spores ; 
this  form  causes  the 
potato  rot.  —  After 
STRASBURGER. 


Then  the  mycelium  sends  its  sporophores  to  the  surface  of 
the  host  (Fig.  30),  for  the  spores  must  be  formed  where  they 
can  be  scattered ;  and  it  is  the  sporophores  coming  to  the 
surface  that  represent  the  only  part  of  trie  parasite  visible 
outside  the  host.  These  spores  are  not  formed  within  spo- 
rangia, but  are  formed  by  cutting  off  the  tip  of  the  sporophore 


THALLOPHYTES 


49 


or  the  tips  of  its  branches  (Fig.  30).  The  sporophores  reach 
the  surface  of  the  host  either  by  emerging  singly  through 
numerous  openings  ("  breathing  pores  ")  in  the  epidermis 


C 

FIG.  31.  —  Downy  mildew:  A,  oogonium  (o)  with  antheridium  (a)  in  contact;  B, 
tube  from  antheridium  penetrating  oogonium ;  C,  oogonium  containing  the  oospore. 
—  After  DEBARY. 

(Fig.  30),  or  by  massing  together  and  pushing  up  the  epider- 
mis until  it  dries  out  and  ruptures.  In  this  latter  case,  the 
first  appearance  on  the  surface  is  a  whitish  blister. 

Later,  the  internal  mycelium  de- 
velops the  sexual  branches,  which  in 
this  case  are  so  different  that  they 
can  be  recognized  as  oogonia  and  an- 
theridia  (Fig.  31).  The  antheridium 
sends  out  a  tube  that  pierces  the  wall 
of  the  oogonium  and  through  which 
the  contents  of  the  antheridium  are 
discharged  into  the  oogonium,  in 
which  the  heavy-walled  oospore  is 
formed  (Fig.  31).  These  sex-organs 
and  the  oospores  are  not  brought  to 
the  surface  of  the  host,  as  are  the 
sporophores,  for  when  the  oospores 
are  ready  to  germinate  during  the 
following  spring,  the  host  tissues  in- 
closing them  have  decayed. 


FIG.  32.  —  Lilac  leaf  covered 
with  mildew:  the  shaded 
regions  representing  the 
mycelium  with  its  numer- 
ous spores  (giving  the 
dusty  appearance) ,  and 
the  black  dots  the  spore- 
cases. 


50 


ELEMENTARY    STUDIES   IN   BOTANY 


Powdery  mildews.  —  There  is  another  group  of  mildews 
(sometimes  called  "  powdery  mildews  "  to  distinguish  them 
from  the  "  downy  mildews  ")  that  will  illustrate 
the  third  relation  of  the  mycelium  to  the  food- 
supply.  One  of  the  most  commonly  observed 
among  them  is  the  lilac  mildew.  It  is  seen 
on  every  lilac  bush  as  whitish,  dusty-looking 
patches  on  the  leaves  (Fig.  32)  ;  in  fact,  whole 
bushes  sometimes  appear  as  if  completely 
covered  by  street  dust.  Under  the  microscope 
it  is  seen  that  this  whitish  material  on  the 
leaves  is  the  mycelium  of  a  fungus,  which  in 
this  case  is  an  external 
parasite.  The  haustoria 
penetrate  the  walls  of  the 
epidermal  cells  of  the  host, 
which  are  really  not  vital 
cells,  so  that  such  mildews 
may  be  very  abundant 
upon  a  plant  without  destroying  it  or  seriously  interfering 
with  its  vigor ;  in  fact,  almost  all  plants  have  mildews. 

The  mycelium  produces  sporo- 
phores  abundantly,  and  it  is  really 
the  numerous  spores  that  give  the 
dusty  appearance  to  the  leaves. 
These  spores  are  formed  as  are 
those  of  the  downy  mildews  de- 
scribed above,  except  that  they 
are  cut  off  in  chains  by  an  un- 
branched  sporophore  (Fig.  33). 

Later  the  sex-organs  appear, 
very  minute  and  not  often  seen, 
but  the  result  of  their  work  is 
always  seen.  This  result  is  a 
heavy- walled  case  (Fig.  34),  which 


FIG.  33.  —  A  sporophore  of  a  mildew  with 
its  row  of  spores.  —  After  TULASNE. 


FIG.  34.  —  A  spore-case  of  a  mil- 
dew, showing  its  heavy  wall,  its 
conspicuous  appendages,  and 
the  sacs  (containing  spores) 
squeezed  out  through  a  break 
in  the  wall. 


THALLOPHYTES 


51 


looks  like  a  brownish  or  blackish  dot  on  the  lilac  leaf  (Fig.  32) . 
When  this  case  is  broken  open,  it  is  found  to  contain  several 
thin- walled  sacs  (sometimes  only  one),  within  which  are 
spores  (Fig.  34).  These  heavy- walled  cases,  always  bearing 
characteristic  "  appendages  "  (Fig.  34),  are  the  protected 
structures  that  last  through  the  winter,  and  it  is  their  spores 
that  start  new  mycelia  during  the  following  spring.  How 
fertilization  results  in  this  case  containing 
sacs  with  spores,  is  not  necessary  for  the 
beginner  to  know. 

The  three  illustra- 
tions given  show  how 
the  mycelium  and  the 
structures  it  produces 
are  related  to  food- 
supply  as  saprophytes 
(as  the  molds) ,  external 
parasites  (as  the  pow- 
dery mildews),  or  in- 
ternal parasites  (as  the 
downy  mildews). 

The  true  Fungi  are 
so  very  numerous  that 
they  cannot  be  pre- 
sented in  a  brief  ac- 
count. It  is  impossible  to  give  examples  even  of  those 
that  are  of  great  economic  importance ;  but  the  above  illus- 
trations will  give  some  idea  of  the  structure  of  the  body  and 
its  relations  to  the  food-supply,  and  two  other  illustrations  are 
added  because  of  their  general  interest. 

Wheat  rust.  —  The  rusts  are  destructive  parasitic  Fungi 
that  attack  very  many  plants,  but  public  interest  is  chiefly 
directed  to  those  that  attack  the  great  cereal  crops,  chief 
among  which  is  wheat.  The  presence  of  rust  in  a  wheat 
field  is  noticed  first  by  the  appearance  of  reddish,  rusty- 


FIG.  35.  —  Summer  spores  of 
the  wheat  rust,  which  form 
the  rusty  lines  on  the 
wheat ;  notice  the  two 
nuclei  in  each  spore. 


FIG.  36.  —  Winter 
spores  of  the 
wheat  rust; 
each  spore  has 
two  cells,  and 
each  cell  has 
two  nuclei. 


52 


ELEMENTARY   STUDIES   IN   BOTANY 


looking  lines  on  the  stem  and  leaves  of  some  of  the  plants. 
These  lines  extend  and  multiply,  new  plants  become  in- 
fected, and  presently  the  whole  field  may  become  rusty.  A 
microscope  shows  that  this  rusty  looking  material  is  made 
up  of  spores  (Fig.  35) ;  and  it  is  evident 
that  they  have  been  brought  to  the  surface 
by  sporophores  arising  from  an  internal 
mycelium. 

Later  in  the  season,  after  the  wheat 
has  been  harvested,  there  appear  black 
lines  on  the  stubble,  the  so-called  "  black 
rust."  It  does  not  belong  to  the  stubble 
any  more  than  to  the  rest  of  the  plant,  but 
it  appears  so  late  in  the  season  that  ordi- 
narily there  is  only  stubble  left  to  appear 


FIG.  37.  —  Winter 
spores  of  the  wheat 
rust  germinating, 
each  filament  con- 
sisting of  four  cells, 
and  each  cell  send- 
ing out  a  delicate 
branch  that  pro- 
duces at  its  tip 
a  spore  (early 
spring  spore).  — 
After  TULASNE. 


FIG.  38.  —  A  cluster-cup  (on  barberry)  of  the  wheat  rust, 
containing  rows  of  spring  spores ;  each  spore  contains 
two  nuclei. 


upon.  The  "  black  rust "  consists  of  heavy- walled  spores  that 
arise  from  the  same  mycelium  (Fig.  36).  There  are  thus 
two  kinds  of  spores  produced  by  the  mycelium  on  the 
wheat ;  one  kind  during  the  season,  by  means  of  which  the 
rust  is  spread ;  the  other  kind  towards  the  end  of  the  season. 


THALLOPHYTES 


53 


by  means  of  which  the  rust  is  carried  through  the  winter. 
Very  naturally,  the  former  are  often  called  " summer  spores" 
(Fig.  35),  and  the  latter  " winter  spores"  (Fig.  36). 

Early  in  the  following  spring  the  winter  spores  germinate, 
producing  very  short  filaments,  and  these  filaments  put  out 
a  few  slender  branches,  at  the  tip  of  each  of  which  a  spore 
is  formed  (Fig.  37).  These  little  filaments  that  produce  the 
third  kind  of  spore  are  not  parasites  at  all,  for  they  are  not 
related  to  any  host.  The  spores  they  produce  may  be  called 
the  "  early  spring  spores." 

The  early  spring  spores  ger- 
minate when  they  fall  upon  the 
right  kind  of  host  plant.  In 
the  wheat  rust  first  studied  in 
England,  the  host  plant  that 
received  the  early  spring  spores 
was  found  to  be  the  barberry. 
The  spores  form  an  extensive 
internal  mycelium  in  the  bar- 
berry leaves,  and  this  mycelium 
sends  to  the  surface  (usually 
the  under  surface)  groups  </ 
sporophores  with  abundant 
spores,  the  groups  forming 
reddish  patches  that  some- 
times cover  the  under  surface 
of  the  leaf  (Fig.  38).  This  is 
the  fourth  kind  of  spore,  and 
may  be  called  the  "  spring 
spore." 

The  spring  spores  that  fall 
upon  young  wheat  plants  germinate  and  form  the  mycelium 
that  feeds  upon  the  wheat,  and  that  produces  the  summer 
and  winter  spores  with  which  this  account  began. 

In  the  life-history  of  wheat  rust,  therefore,  there  are  four 
5 


FIG.  39.  —  Mycelium  of  a  mushroom 
producing  sporophores  (young 
mushrooms,  called  "buttons"). — 
After  SACHS. 


54  ELEMENTARY   STUDIES   IN   BOTANY 

kinds  of  spores,  three  kinds  of  mycelia  (two  of  which  are 
parasitic),  and  two  different  hosts.  This  probably  represents 
the  most  complex  life-history  of  a  fungus,  and  illustrates  the 
great  difficulty  of  studying  and  combating  the  rusts.  Of 
course,  the  rusts  that  attack  the  wheat  fields  of  the  United 
States  do  not  use  usually  the  barberry  as  the  "  intermediate 
host,"  since  with  us  barberry  bushes  are  not  common  enough 
to  serve  such  a  purpose.  But  our  several  kinds  of  rusts  use 


FIG.  40.  —  A  common  edible  mushroom ;   really  a  sporophore. 

other  intermediate  hosts,  which  are  plentiful  enough  to  in- 
sure a  continuation  of  the  rust. 

Mushrooms.  —  Even  a  very  short  account  of  Fungi  would 
be  incomplete  without  some  mention  of  the  mushrooms, 
which  are  perhaps  the  Fungi  best  known  to  most  people. 
There  is  no  difference  between  mushrooms  and  toadstools, 
except  that  the  latter  name  has  been  applied  to  those  mush- 
rooms that  are  poisonous.  Very  closely  related  mushrooms 
may  differ  in  this  particular,  so  that  the  two  names  cannot  be 
used  as  terms  of  classification.  For  example,  Boletus  edulis, 


THALLOPHYTES 


55 


as  its  name  implies,  is  an  edible  form  ;  while  its  near  relative, 
Boletus  Satanas,  as  its  name  implies,  is  a  deadly  form. 

The  mycelium  of  a  mushroom  extends  widely  in  the  decay- 
ing material  in 
which  it  grows 
(Fig.  39).  In 
some  cases  it  ex- 
tends under  the 
bark  of  trees  and 
does  them  great 
damage.  Every 
one  must  have 
seen  these 
thready  growths 
in  forest  soil  or 
in  rotting  logs 
and  stumps. 
This  mycelium 
sends  up  sporo- 
phores, which  are 
the  structures 
commonly  called 
mushrooms  (Fig. 
40).  They  differ 
from  the  ordi- 
nary sporophores 
of  Fungi  in  con- 
sisting of  many 

branches     Orgr.n- 

i-7orl     tnn-o+Vior    in 
T/0&ei 

a  Complex  Struct- 

ure.  They  may 
be  called  "  compound  "  sporophores,  to  distinguish  them 
from  the  simple  sporophores  of  the  other  groups.  These 
sporophores  produce  a  vast  number  of  spores  (Fig.  41), 


FIG.  41.  —  Sections  through  gills  of  a  mushroom  :  A,  gills 
hanging  from  the  cap  (pileus)  ;  B,  single  gill  enlarged, 
showing  the  basidium  layer  ;  C,  much  enlarged  view 
°^  a  Portion  °f  a  basidium  layer,  showing  the  basidia 
bearing  spores.  —  After  SACHS. 


56 


ELEMENTARY    STUDIES   IN  .BOTANY 


which  on  germination  produce  new  mycelia,  so  that  the 
life-history  of  a  mushroom  is  very  simple  compared  with 
that  of  a  rust. 

These  sporophores  are  not  always  of  the  umbrella-form 
commonly  associated  with  the  name  mushroom.  Very  often 
they  form  brackets  on  stumps  and  tree  trunks  (Fig.  42) ; 


FIG.  42.  —  A  bracket  fungus  growing  on  a  red  oak. 

sometimes  they  are  merely  like  incrustations;  while  in  the 
so-called  "  puff-balls  "  they  are  globular  (Fig.  43). 

The  groups  of  true  Fungi.  —  There  are  three  great  groups 
of  true  Fungi  recognized,  which  may  be  denned  briefly  as 
follows. 

In  the  first  group  the  mycelium  has  no  cross  walls,  except  as 


THALLOPHYTES 


57 


sporangia  or  spores  or  sex-organs  are  cut  off  from  the  rest  of 
the  body ;  and  therefore  the  vegetative  body  is  one  continu- 
ous cavity.  It  is  the  one  group  of  Fungi  that  can  be  recog- 
nized from  its  mycelium.  The  sexual  apparatus  very  much 
resembles  that  of  the  Algae,  and  the  whole  structure  of  the 
body  is  so  suggestive  of  Alga3  that  if  these  were  the  only 
Fungi  probably  no  one  would  doubt  that  Fungi  had  been 
derived  from  Algae.  On 
account  of  this  resem- 
blance, the  group  is  called 
the  "  Alga-fungi  "  (Phy- 
comycetes).  Among  the 
illustrations  used  above, 
the  molds  and  downy 
mildews  are  members  of 
this  group. 

In  the  second  group  the 
mycelium  has  cross  walls, 
but  the  sex-apparatus,  so 
far  as  any  has  been  found, 
is  not  very  suggestive  of 
the  Alg33.  The  distin- 
guishing mark  of  the 
group,  however,  is  the  pro- 
duction of  spores  within 
a  sac  that  has  a  peculiar 

origin.  Therefore  the  group  is  called  the  "  Sac-fungi  " 
(Ascomycetes) ,  and  the  lilac  mildew,  mentioned  above,  is 
a  member  of  it.  In  that  plant  the  spore-containing  sac 
(ascus)  is  inclosed,  usually  along  with  others,  by  a  case 
(Fig.  34),  but  in  many  Sac-fungi  the  case  does  not  inclose 
the  sacs,  but  forms  disks,  cups,  funnels,  or  flasks,  which  the 
sacs  line.  Any  fungus  in  whose  life-history  these  sacs  appear 
is  a  "  Sac-fungus." 

In  the  third  group  the  mycelium  has  cross  walls,  as  in  the 


FIG.  43.  —  Puffballs.  —  After  GIBSON. 


58 


ELEMENTARY   STUDIES   IN   BOTANY 


second,  but  the  spores  are  formed  at  the  ends  of  slender 
branches  that  arise  from  a  peculiar  cell  or  group  of  cells 


FIG.  44.  —  A  lichen  growing  on  bark ;  the  numerous  dark  disks  are  cup-like  spore-cases. 

called   the   basidium    (Fig.    41).     These   are   therefore   the 
"  Basidium-fungi  "  (Basidiomycetes) ,  and  the  wheat  rust  and 


FIG.  45.  —  A  lichen  growing  on  a  board. 

mushrooms  are  members  of  it.     Any  fungus  in  whose  life- 
history  basidia  appear  is  a  "  Basidium-fungus." 


THALLOPHYTES 


59 


Perhaps  the  best  definition  of  the  first  group  (Phycomy- 
cetes)  is  that  it  includes  all  true  Fungi  in  whose  life-histories 
neither  asci  nor  basidia  appear. 

39.  Lichens.  —  Lichens  are  very  commonly  observed 
plants,  forming  splotches  of  various  colors  on  tree  trunks, 
rocks,  old  boards,  etc.,  and  growing  also  upon  the  ground. 
They  may  resemble  in- 
crustations on  these  va- 
rious supports ;  or  they 
may  have  very  definite 
flat  and  lobed  bodies 
that  are  not  attached 
throughout  to  their  sup- 
ports (Figs.  44  and  45) ; 
or  they  may  have  slen- 
der, branching  bodies 
that  are  erect,  hanging, 
or  prostrate.  The  so- 
called  " reindeer  moss" 
is  an  erect,  branching 
lichen  common  in  north- 
ern latitudes ;  and  in 
certain  mountain  re- 
gions trees  are  fre- 
quently thickly  covered 
with  the  hanging  lichens 
(Fig.  46). 

The  most  important  fact  about  a  lichen  is  that  it  is  made 
up  of  two  very  different  plants,  a  fungus  and  an  alga ;  but 
these  two  are  so  closely  associated  that  they  seem  to  belong 
to  a  single  body  (Fig.  47).  In  fact,  a  lichen  is  a  parasitic 
fungus  that  obtains  its  food-supply  from  certain  Algae,  and 
in  doing  so  inwraps  the  Algae  completely.  Apparently  the 
Algae  are  not  injured,  and  in  fact  their  position  in  the  midst 
of  a  moist,  sponge-like  body  is  very  favorable  for  their  work. 


FIG.  46.  —  A  hanging    and    profusely  branching 
lichen.  —  After  SACHS. 


60 


ELEMENTARY   STUDIES   IN   BOTAN1 


This  means  that  in  this  position  the  Algae  manufacture  food 
enough  for  themselves  and  for  the  fungus,  for  otherwise  they 
would  be  destroyed. 

This  association  has  led  to  some  very  important  results.  It 
makes  it  possible  for  the  two  plants  to  exist  in  conditions  that 
would  be  impossible  for  either  plant  alone.  For  example, 

lichens  are  abundant  on 
bare  rocks,  from  which 
all  other  plants  are 
absent.  In  ascending 
mountains,  after  all  other 
vegetation  has  disap- 
peared, the  lichens  per- 
sist on  the  most  exposed 
rocks.  In  such  places 
the  alga  could  not  grow 
alone  because  of  lack  of 
moisture,  and  the  fungus 
could  not  grow  alone  be- 
cause of  lack  of  food; 
but  in  the  sponge-like 
body  of  the  fungus  the 
alga  gets  its  moisture, 
and  from  the  enmeshed 
alga  the  fungus  gets  its 
food.  This  fact  is  im- 
portant, because  lichens  can  thus  start  soil-formation  on 
bare  and  exposed  surfaces.  The  materials  of  their  dead 
bodies  give  to  other  plants  a  chance  to  grow,  and  so  a  soil 
gradually  accumulates. 

At  certain  times  disk-like  or  cup-like  bodies  are  borne  by 
lichens,  with  brown  or  black  or  more  brightly  colored  lining 
(Figs.  44  and  45).  When  this  lining  is  examined,  it  is  found 
to  be  made  up  largely  of  delicate  sacs  containing  spores 
(Fig.  48).  This  shows  that  the  lichen  fungus  is  a  sac-fungus 


FIG.  47.  — -  Section  of  a  lichen,  showing  the  in- 
terwoven mycelium  of  the  fungus  (m)  and 
the  enmeshed  alga  (g).  —  After  SACHS. 


THALLOPHYTES  61 

(Ascomycete),  and  that  a  lichen  is  simply  a  sac-fungus  para- 
sitic on  Algae.  With  very  few  exceptions,  all  lichens  are 
Sac-fungi. 

40.  Soil  Fungi.  —  Before  leaving  the  Fungi,  further  ref- 
erence should  be  made  to  the  part  they  play  in  the  soil. 
The  work  of  bacteria  in  the  soil  was  referred  to  in  a  preced- 
ing section  (§  37,  p.  46),  but  true  Fungi  are  important 
also. 

The  soil  must  not  be  thought  of  as  simply  an  accumulation 
of  "  dirt,"  but  as  material  very  full  of  life.  Just  as  the  waters 


FIG.  48.  —  Section  of  the  cup-like  spore-case  of  a  lichen,  showing  the  lining  layer  of 
sacs  containing  spores  (h) ;  the  tangle  of  the  mycelium  (m)  and  the  groups  of 
Algse  (g)  may  be  seen.  - —  After  SACHS. 

are  spoken  of  as  "  swarming  with  life,"  so  are  the  soils 
"  swarming  with  life,"  chiefly  Fungi.  What  makes  this 
fact  important  is  that  the  soil  Fungi  are  important  factors  in 
making  the  soil  suitable  for  plants.  The  nature  of  the  work 
accomplished  by  these  soil  Fungi,  in  relation  to  the  use  of 
soil  by  plants,  may  be  outlined  as  follows. 

In  speaking  of  the  manufacture  of  proteins  (§  29,  p.  37),  the 
statement  was  made  that  in  connection  with  this  process  com- 
pounds containing  nitrogen  must  enter  the  plant.  In  the 
case  of  soil  plants,  these  compounds  are  obtained  from  the 


62 


ELEMENTARY    STUDIES   IN   BOTANY 


soil  in  the  form  of  salts  called  nitrates,  which  are  soluble  and 
therefore  "  available."     It  is  evident  that  when  crops  are 


FIG.  49.  —  Root-tubercles  on  sweet  clover. 


removed  from  the  soil,  a  large  amount  of  nitrogen  compounds 
is  removed  also,  so  that  crops  drain  nitrogen  from  the  soil. 
This  cannot  go  on  indefinitely,  without  fresh  supplies  of 


THALLOPHYTES  63 

nitrogen  for  protein  manufacture.  This  is  what  is  often 
meant  when  a  soil  is  said  to  be  "  impoverished." 

There  are  at  least  two  general  ways  by  which  fresh  supplies 
of  available  nitrogen  are  being  added  to  the  soil  continuously, 
and  the  agents  in  both  cases  are  bacteria.  One  way  is  to 
obtain  nitrates  (nitrogen  in  its  available  form  for  plants) 
from  the  decay  of  organic  matter,  and  whole  series  of  bac- 
teria are  active  in  the  various  steps  of  this  process.  There- 
fore, as  bodies  of  plants  and  animals  die,  or  leaves  and 
branches  fall,  or  manure  is  spread  on  the  soil,  relays  of  bac- 
teria lay  hold  of  this  material,  and  among  the  products  of 
their  activity  are  the  nitrates. 

The  other  way  is  to  use  the  free  nitrogen  of  the  air  in  the 
manufacture  of  nitrates,  and  certain  bacteria  are  the  agents 
in  this  remarkable  process.  It  is  an  interesting  fact  that 
although  the  air  is  about  four-fifths  free  nitrogen,  and  that 
plants  are  therefore  living  submerged  in  an  ocean  of  nitrogen, 
they  cannot  use  it  in  this  free  form,  that  is,  it  is  not  available. 
But  the  soil  bacteria  referred  to  are  very  exceptional  among 
plants  in  the  power  to  use  free  nitrogen  (soil  water  contains 
free  nitrogen  in  solution),  probably  in  the  manufacture  of 
their  proteins.  This  work  results  in  more  organic  material 
containing  nitrogen  to  become  the  source  of  nitrates.  These 
"  nitrogen-fixing  "  bacteria^  as  they  are  called,  work  conspicu- 
ously in  connection  with  the  clovers,  alfalfa,  etc.,  on  whose 
roots  they  form  little  swellings  ("  tubercles,"  Fig.  49),  and 
from  which  they  obtain  carbohydrate  food.  The  clovers  in 
turn  consume  the  bacteria,  and  if  the  clover  crop  is  plowed 
under  ("  green  manuring  "),  a  large  amount  of  nitrogen- 
containing  material  is  added  to  the  soil,  whose  nitrogen  came 
from  the  air  by  way  of  the  nitrogen-fixing  bacteria. 

These  two  kinds  of  work  partially  explain  why  the  soil 
improves  when  a  field  "  lies  fallow  "  (is  not  used),  and  why  it 
is  of  advantage  to  alternate  a  clover  or  alfalfa  crop  with 
other  kinds  of  crops  ("  rotation  of  crops  ").  In  the  former 


64 


ELEMENTARY    STUDIES   IN   BOTANY 


case,  the  loss  of  nitrogen  is  stopped  and  nitrates  are  allowed 
to  accumulate ;  in  the  latter  case,  fresh  drafts  on  the  air, 
the  ultimate  source  of  nitrogen,  are  made.  There  are  other 
reasons  why  a  soil  improves  by  "  resting  "  or  by  a  clover 
crop,  but  these  will  be  referred  to  when  the  crop  plants  are 
studied.  In  this  connection  we  are  merely  concerned  with 
the  work  of  Fungi  in  the  soil. 

The  true  Fungi  of  the  soil,  with  their  network  of  filaments 
extending  everywhere  through  the  soil,  have  proved  to  be 

of  much  greater  importance  than 
was  once  supposed.  These  subter- 
ranean mycelia  become  connected 
with  the  roots  of  many  plants  (Fig. 
50),  from  which  they  obtain  their 
food-supply,  and  in  so  doing  put  at 
the  service  of  the  host  plant  an  ex- 
tensive water-receiving  and  salt- 
receiving  system.  Such  plants  as 
orchids  and  oaks  have  long  been 
notorious  for  using  subterranean 
mycelia  in  this  way,  but  it  is  found 
now  that  this  arrangement  is  of 
great  advantage  to  any  plant. 
Especially  does  this  habit  prevail 
in  forest  soil,  which  is  "  a  living  mass  of  innumerable 
filamentous  Fungi."  In  effect,  this  connection  established 
between  an  oak,  for  example,  and  the  subterranean  mycelia, 
resembles  the  establishment  of  a  connection  between  the  pipe 
systems  of  a  house  and  those  of  a  city.  With  such  a  con- 
nection, soil  water  and  soil  salts  far  beyond  the  reach  of  the 
root  system  of  a  plant  become  available.  Such  Fungi  are 
called  mycorhiza,  a  name  meaning  "  root-fungi." 

41.  Summary.  —  The  Fungi  are  Thallophytes  that  can- 
not manufacture  food,  and  therefore  are  dependent  plants. 
The  dependent  habit  compels  them  to  obtain  food  as 


FIG.  50.  —  Mycorhiza  :  the  tip 
of  a  beech  rootlet  enmeshed  by 
a  soil  fungus.  —  After  FRANK. 


THALLOPHYTES  65 

parasites  or  saprophytes,  and  therefore  they  are  of  great 
economic  importance.  They  may  be  very  useful,  as  are  the 
soil  Fungi,  or  they  may  be  very  injurious,  as  are  the  disease- 
producing  Fungi. 

The  bodies  of  Fungi  range  from  single  cells  (as  the  Bac- 
teria) to  filamentous  bodies  (the  mycelia  of  true  Fungi), 
and  many  of  the  higher  forms  become  quite  complex.  The 
reproductive  methods  are  also  the  same  as  those  of  Algae; 
namely,  vegetative  multiplication,  spore-reproduction,  and 
sexual-reproduction  with  its  differentiations.  But  among 
the  higher  Fungi  the  sexual-reproduction  becomes  less  and 
less  obvious,  and  in  some  cases  it  may  have  disappeared. 

While  the  Algae  may  be  said  to  represent  the  foundation 
upon  which  the  plant  kingdom  has  been  built,  the  Fungi 
hold  no  relation  to  the  higher  groups.  In  the  history  of 
the  plant  kingdom,  therefore,  the  Algae  are  much  more  im- 
portant than  the  Fungi ;  but  in  the  economic  interests  of 
man,  the  Fungi  are  much  more  important  than  the  Algae. 


CHAPTER   V 
BRYOPHYTES 

THE  FIRST  LAND  PLANTS 

42.  Problem  of  the  land  habit.  —  It  was  stated  that  Algae 
live  exposed  to  water  as  a  medium,  and  that  their  structures 
and  habits  are  explained  by  this  fact.  To  live  on  the 
land  means  exposure  to  air  as  a  medium,  and  the  structures 
and  habits  of  land  plants  are  explained  by  this  fact.  The 
danger  of  exposure  to  air  is  the  loss  of  water  by  the  plant. 
It  must  lose  water  to  the  drying  air,  and  unless  there  is  some 
check,  the  loss  will  be  greater  than  the  supply,  and  death 
will  ensue. 

When  an  alga  is  removed  from  water  and  exposed  to  air, 
it  dries  out  quickly  and  perishes,  for  there  is  no  check  to  the 
very  rapid  loss  of  water  from  the  protoplasts.  Therefore, 
if  water  plants  are  to  become  land  plants,  they  must  acquire 
the  air-habit  by  developing  protective  structures.  It  is 
believed  that  this  is  just  what  certain  Algse  did,  and  that  in 
so  doing  they  became  so  different  in  structure  that  they 
ceased  to  be  Algae.  In  any  event,  the  acquiring  of  the 
land-habit  was  about  the  most  important  happening  in  the 
history  of  plants,  for  it  made  possible  all  the  subsequent 
progress  of  the  plant  kingdom. 

One  may  picture  how  a  gradually  increasing  exposure  to 
air  might  have  occurred,  beginning  with  occasional  exposures 
on  muddy  flats,  and  by  gradual  shoreward  migration,  ending 
in  continual  exposure.  Even  when  exposure  to  air  became 
continual,  it  must  have  been  for  a  long  time  in  conditions  of 


BRYOPHYTES  67 

shade  and  moisture,  for  life  "  in  the  open  "  means  extreme 
danger  from  loss  of  water. 

43.  The  Liverworts.  —  This  group  of  plants  is  not  con- 
spicuous, and  therefore  it  is  not  noticed  by  most  people, 
but  it  is  believed  to  be  the  group  that  acquired  the  land- 
habit  and  that  has  given  rise  to  all  the  higher  plants.     The 
Liverworts,  therefore,  are  of  very  great  historical  importance, 
and  should  be  known,  by  sight  at  least,  to  every  student  of 
plants.     They  may  be  called  the  amphibians  of  the  plant 
kingdom,  for  they  connect  the  water  forms  with  the  land 
forms. 

Although  Liverworts  solved  the  problem  of  living  on  land, 
they  give  one  the  impression  of  being  on  the  defensive  against 
the  air  rather  than  of  using  the  air  and  sunshine  freely.  For 
the  most  part,  they  occur  in  moist  places,  or  at  least  in  shaded 
places.  It  is  one  thing  to  live  in  protected  places,  and  a  very 
different  thing  to  live  and  work  in  the  open.  To  occupy 
the  general  land  surface  means  that  many  plants  must  live 
in  unprotected  places,  and  it  remained  for  the  higher  plants 
to  solve  this  problem,  by  substituting  protective  structures 
and  habits  for  protected  places. 

There  are  two  general  facts  in  this  connection  that  should 
be  kept  in  mind.  One  is  that  a  plant  may  work  in  a  pro- 
tected place,  but  the  opportunities  for  work  are  not  so  great. 
The  progress  of  plants,  therefore,  implies  that  they  must 
acquire  the  ability  to  use  the  largest  opportunities.  An- 
other fact  is  that  work  and  endurance  are  not  the  same 
thing.  Plants  may  endure  conditions  of  exposure,  but  not 
be  able  to  work  except  so  far  as  it  is  necessary  to  maintain 
life.  An  ordinary  deciduous  tree  endures  the  winter,  but  it 
works  in  the  summer.  In  considering  the  progress  of  plants, 
therefore,  it  is  not  a  question  of  the  conditions  which  they 
can  endure,  but  of  the  conditions  in  which  they  can  work. 

44.  The  body  of  Liverworts.  —  If  Liverworts  are  Algae 
that  have  acquired  the  land-habit,  it  is  important  to  know 


68 


ELEMENTARY   STUDIES   IN   BOTANY 


something  of  the  structure  of  the  body  that  can  resist  the 
drying  air.  It  is  evident  that  an  ordinary  filamentous  alga, 
with  every  cell  freely  exposed,  could  not  endure  long  expos- 
ure to  the  air.  But  the  bodies  of  certain  Algae  are  flat 


FIG.  51.  —  Riccia:  a  group  of  floating  Liverworts,  showing  the  dorsal  surface  exposed 
to  light ;  the  flat  body  forks  as  it  grows,  and  the  axis  of  each  branch  is  marked  by 
a  deep  groove,  in  the  bottom  of  which  the  sex-organs  (antheridia  and  archegonia) 
occur.  —  Photograph  by  LAND. 

plates  of  cells,  and  such  bodies  seem  to  have  supplied  the 
start  for  Liverworts.  A  brief  description  of  a  liverwort 
body  will  show  how  every  fact  is  related  to  air  exposure  as 
contrasted  with  water  exposure. 

The  body  is  compact ;  that  is,  the  cells  are  close  together, 


BRYOPHYTES 


69 


forming  a  sheet  of  cells.  In  this  way,  only  two  sides  of  a  cell 
are  exposed,  and  if  the  sheet  of  cells  is  more  than  one  layer 
thick,  as  is  usual  among  Liverworts,  the  outside  cells  have 
one  side  exposed,  and  the  cells  within  are  not  exposed  at  all. 

The  body  lies  flat,  so  that  only  the  upper  surface  is  ex- 
posed freely  to  the  air  (Fig.  51).  This  position,  added  to 
the  fact  that  the  body  is  usually  lying  upon  a  moist  surface, 
results  in  the  least  possible  amount  of  danger  from  exposure 
to  the  drying  air.  Since  the  liverwort  body  may  be  lying 
upon  rock  or  soil  or  a  tree 
trunk,  it  is  convenient  to 
have  a  general  term  to 
express  the  surface  upon 
which  it  rests,  and  this 
term  is  substratum.  The 
liverwort,  therefore,  is 
prostrate  upon  its  sub- 
stratum, and  this  position 
results  in  a  dorsiventral 
body,  which  means  that 
the  body  has  two  unlike 
surfaces,  the  dorsal  and 
the  ventral.  In  the  liver- 
wort, the  dorsal  surface  is 
exposed  to  air  and  sunlight,  while  the  ventral  surface  is  in 
contact  with  the  substratum.  It  is  these  two  different 
kinds  of  exposure  that  result  in  the  two  surfaces  being 
unlike.  An  ordinary  leaf  is  a  dorsiventral  organ,  with 
the  two  surfaces  differently  exposed  and  hence  different 
in  structure. 

When  the  liverwort  body  is  several  layers  of  cells  thick, 
the  outermost  layer  of  cells  is  modified  and  becomes  the 
protective  layer  known  in  all  plants  and  animals  as  the 
epidermis  (Fig.  52).  The  cells  of  the  epidermis  differ  from 
the  other  cells  of  the  body,  and  the  differences  make  the 
6 


FIG.  52.  —  Marchantia :  section  through  the 
body,  showing  the  epidermis  above  and 
below  (the  upper  and  more  exposed  epi- 
dermal layer  especially  distinct),  the  air- 
chamber  into  which  project  special  cells 
containing  chloroplasts,  the  air-pore  (with 
its  chimney-like  arrangement  of  cells) 
opening  through  the  epidermis  into  the 
air-chamber,  and  the  layers  of  compara- 
tively colorless  cells  between  the  air- 
chamber  and  the  lower  epidermis. 


70 


ELEMENTARY    STUDIES   IN   BOTANY 


epidermis  very  resistant  to  the  passage  of  water  from  the 
interior  of  the  plant  to  the  surface.  In  other  words,  the 
epidermis  is  in  effect  a  waterproof  layer,  not  to  prevent 
water  from  entering  the  plant,  but  to  prevent  water  from 
leaving  the  plant. 

A  compact,  prostrate  (dorsiventral)  body,  ensheathed  by 
an  epidermis,  is  well-equipped  for  exposure  to  the  air,  es- 

pecially if  the  air  is  not 
very  dry. 

The  dorsiventral  posi- 
tion develops  differences 
in  different  regions  of  the 
body.  The  dorsal  side  of 
the  body  is  exposed  to 
light,  and  as  the  light 
reaches  the  cells,  chloro- 
phyll is  formed,  and  such 
cells  are  equipped  for 
photosynthesis  (Fig.  52). 

^  J 

If  the   body  is  Very  thin, 
,.    ,    .  . 

cups  containing  gemma;  ;  the  rhizoids  arising  light  may  penetrate  it 
from  the  ventral  surface  are  also  shown  ;  B,  nnrrmlptplv  anH  all  thp 
a  section  through  a  part  of  one  of  the  disks,  j61^'  £ 

showing  the  short-stalked  antheridia  in  flask-       cells  will    be    green.       But 
shaped  'cavities  that  open  on  the  upper  sur- 
face  of  the  disk  ;    C,  the  outline  of  a  gemma.       Ordinarily  the   body  IS  SO 

thick  that  light  of  suffi- 

cient intensity  does  not  penetrate  through  it,  so  that  a 
certain  number  of  layers  of  cells  on  the  ventral  side 
may  not  contain  chlorophyll  (Fig.  52).  In  this  way  the 
body  is  differentiated  into  two  regions  :  a  dorsal  region 
of  green  cells  doing  the  work  of  carbohydrate  manufac- 
ture; and  a  ventral  region  of  colorless  cells.  Another 
form  of  differentiation  is  seen  in  the  structures  produced 
by  the  two  surfaces.  The  dorsal  surface,  with  its  free 
exposure  to  the  air,  develops  the  sex-organs  and  spores, 
for  the  spores  are  dispersed  by  currents  of  air  (Figs.  53  and 


FIG.  53.  —  Marchantia:  A,  a  plant  bearing  on 
its  dorsal  surface  three  long-stalked  disks 
containing  antheridia,  and  also  two  small 


BRYOPHYTES 


71 


54).  The  ventral  surface  puts  out  hair-like  processes  that 
grip  the  substratum  (Figs.  53  and  54).  These  hairs  are 
called  rhizoids,  which  means  "  root-like,"  but  they  are  not 
like  roots.  They  have  not  the  structure  of  roots,  and  they 
do  not  perform  the  work  of  roots  except  as  they  anchor  the 
body. 

This  differentiation  of  the  body,  compelled  by  its  position, 
outlines  regions  of  work  that  become  more  definite  in  higher 
plants.  Water  enters  the 
body  through  the  lower  epi- 
dermis, is  conducted  through 
the  polorless  cells  on  the  ven- 
tral side,  is  brought  to  the 
green  cells  on  the  dorsal  side, 
and  is  partly  used  there  in 
food  manufacture.  It  must 
not  be  supposed  that  all  of 
the  water  that  enters  a  plant 
is  used  in  photosynthesis,  for 
the  bulk  of  it  keeps  the  pro- 
toplasts of  all  the  cells  in  a 
condition  for  working,  and 
the  protoplasts  are  losing  it 
all  the  time  to  the  air.  The 
problem  of  the  plant  is  to 
see  to  it  that  the  protoplasts 
do  not  lose  water  faster  than  it  is  supplied.  The  picture 
in  one's  mind,  therefore,  should  be  that  of  a  stream  of 
water  moving  continuously  through  the  body  of  the  plant, 
primarily  to  keep  it  in  working  condition,  and  incidentally  to 
supply  a  little  for  photosynthesis. 

The  epidermis  introduced  a  new  problem  which  the  Liver- 
worts and  all  the  higher  green  plants  have  solved.  In  order 
to  do  their  peculiar  work,  the  green  cells  must  be  exposed  to 
the  air,  from  which  carbon  dioxide  is  obtained,  and  to  which 


FIG.  54. — -Marchantia:  a  plant  bearing 
on  its  dorsal  surface  three  long-stalked 
disks  with  finger-like  lobes  and  contain- 
ing archegonia,  and  also  two  small  cups 
containing  gemmae  ;  the  archegonia  are 
found  on  the  ventral  side  of  the  disk, 
hanging  from  the  angles  between  the 
lobes. 


72 


ELEMENTARY    STUDIES   IN   BOTANY 


oxygen  is  given.  The  waterproofing  epidermis  interferes 
with  this  exchange,  and  therefore  it  must  be  interrupted 
enough  to  let  the  air  into  the  green  cells.  In  the  simpler 
Liverworts  these  openings  for  the  air  are  secured  by  clefts, 
while  in  complex  Liverworts  there  are  elaborate  pores  in 

the  epidermis,  that  open 
into  internal  air  chambers 
(Fig.  52).  In  this  latter 
case  there  is  an  internal 
atmosphere  that  bathes 
the  green  cells,  which 
communicates  with  the 
external  atmosphere 
through  the  pores.  In 
this  way  the  gas  exchange 
is  provided  for ;  but  the 
pores  also  open  up  a  way 
for  the  escape  of  water 
vapor  from  the  inner  cells. 
This  loss  of  water  is  the 
price  the  plant  must  pay 
for  the  opportunity  to 
manufacture  food. 

The  bodies  of  Liver- 
worts have  advanced  in 
two  general  directions. 
Some  Liverworts  have 
retained  the  primitive 

form  of  the  body,  a  continuous  sheet  of  cells  which  branches 
by  forking,  and  have  advanced  in  making  the  structure  of 
the  body  more  and  more  complex  (Fig.  51).  Other  Liver- 
worts, and  these  are  far  more  numerous,  have  retained  the 
simple  structure  of  the  body,  and  have  advanced  in  changing 
the  form  of  the  body,  so  that  the  flat  sheet  becomes  dif- 
ferentiated into  a  central  axis  (stem)  bearing  many  lobes  of 


FIG.  55.  —  Porella,  a  leafy  liverwort :  A,  a  plant 
showing  the  two  rows  of  overlapping  dorsal 
leaves,  and  also  three  special  branches  that 
bear  antheridia ;  B,  a  plant  with  the  special 
branches  that  bear  archegonia  (two  of  these 
branches  are  bearing  the  spore-cases  produced 
by  the  fertilized  egg)  ;  C,  ventral  view  of  a 
plant,  showing  the  ventral  leaves  much 
modified  by  being  in  contact  with  the 
substratum. 


BRYOPHYTES 


75 


swimming  (Fig.  57).  It  is  an  interesting  fact  that  the  spores 
became  related  promptly  to  air  dispersal,  but  that  the  sperms 
retained  the  water  habit  of  swimming.  This  means  that  the 
act  of  fertilization  can  take  place  only  in  the  presence  of 
water,  so  that  if  a  liverwort  is  kept  from  free  water,  fertiliza- 
tion does  not  occur.  It  must  be  remembered,  however,  that 
even  "  a  film  of  dew  "  is  sufficient  water  for  the  swimming  of 
such  sperms. 

Among  the  Algae,  the  female  sex-organ  was  called  an 
oogonium,  but  among  the  Liverworts  and  all  higher  plants 
it  is  called  an  archegonium.  It  is  so 
constant  in  appearance  that  it  is  rec- 
ognized easily  in  any  group  in  which 
it  occurs  (Fig.  58).  The  protective 
jacket  forms  a  flask  with  a  more  or 
less  slender  neck,  and  in  the  body  of 
the  flask  the  egg  is  formed.  The  two 
regions  of  an  archegonium,  therefore, 
are  the  neck,  through  which  the  sperms 
pass  to  reach  the  egg,  and  the  venter 
(the  body  of  the  flask)  in  which  the 
egg  lies. 

When  the  water  conditions  are  favor- 
able, the  sperms  swim  to  the  archegonia, 
enter  the  necks,  reach  the  eggs,  and 
fuse  with  them,  and  the  result  is  a  fertilized  egg  (oospore)  in 
each  archegonium. 

46.  Alternation  of  generations.  —  A  most  important  fact 
in  connection  with  Liverworts  remains  to  be  told.  Among 
the  ordinary  Algse,  the  fertilized  egg,  just  as  the  spore, 
produces  a  plant  like  that  from  which  it  came,  so  that  the 
life-history  formula  (§  17,  p.  24)  is  Pn2>o— P.  But  when 
the  fertilized  egg  of  a  liverwort  germinates,  it  produces 
a  very  different  kind  of  plant.  This  new  kind  of  individual 
is  a  spore-case,  which  in  most  Liverworts  has  a  stalk,  and  the 


FIG.  58.  —  Marchantia:  an 
archegonium,  showing  the 
long  neck,  and  the  venter 
containing  the  egg. 


76  ELEMENTARY   STUDIES   IN   BOTANY 

stalk  may  be  very  long.  This  spore-case  individual  is  usually 
without  chloroplasts,  so  that  it  cannot  manufacture  food. 
It  obtains  food  from  the  plant  that  produced  the  egg,  usually 
by  the  end  of  its  stalk  becoming  imbedded  in  the  tissue  of 
that  plant.  This  imbedded  part  of  the  stalk  often  be- 
comes enlarged  and  is  called  the  foot,  and  it  is  through  the 
foot  that  food  enters  the  spore-case  individual,  which  is 
therefore  a  parasite. 

When  the  spores  formed  by  this  individual  germinate,  they 
do  not  produce  other  spore-case  individuals,  but  they  pro- 
duce the  green  liverwort  body. 

The  life-history  of  a  liverwort,  therefore,  includes  two  in- 
dividuals that  alternate  with  one  another.  One  individual 
is  green  and  bears  the  sex-organs  (containing  gametes),  and 
hence  is  called  the  gametophyte  ("  gamete-plant  ") ;  the  other 
is  a  parasite  and  produces  spores,  and  hence  is  called  the 
sporophyte  ("  spore-plant  ").  The  fertilized  egg  of  the  game- 
tophyte produces  the  sporophyte,  and  the  spore  of  the  sporo- 
phyte in  turn  produces  the  gametophyte.  The  life-history 
formula,  using  G  for  gametophyte  and  S  for  sporophyte, 
thus  becomes  G=2>o — S — o — G=£>  o — S,  etc.  This  is  alter- 
nation of  generations,  meaning  that  two  individuals  (gen- 
erations) alternate  in  the  life-history.  This  is  a  most 
important  fact  in  connection  with  Liverworts,  because  all 
of  the  higher  plants  continue  this  alternation,  and  their 
advance  has  depended  upon  the  modification  of  these  two 
generations.  It  must  not  be  supposed  that  Liverworts 
introduced  alternation  of  generations,  for  it  was  started  among 
Algae,  but  Liverworts  established  it,  and  all  plants  afterwards 
retained  it. 

It  will  be  noticed  that  alternation  of  generations  involves 
a  division  of  labor.  Among  Algae  that  do  not  possess  it, 
the  same  individual  manufactures  food,  produces  spores, 
and  forms  gametes.  In  Liverworts,  the  gametophyte  manu- 
factures food  and  forms  gametes,  while  the  sporophyte 


BRYOPHYTES 


77 


produces  spores.  The  gametophyte  is  the  more  conspicu- 
ous generation  on  account  of  food  manufacture,  which  de- 
mands a  display  of  green  tissue,  and  therefore  among  Liver- 
worts the  gametophyte  is  thought  of  usually  as  "  the  plant," 
and  the  sporophyte  as  its  "  fruit."  Of  course  the  sporo- 
phyte  is  in  no  sense  a  "  fruit,"  for  it  has  no  more  connection 
with  the  gametophyte  than  a  parasite  has  with  its  host. 

Since  gametophytes  and  sporophytes  will  be  changing 
in  appearance  and  relative  prominence  as  we  proceed  through 
the  higher  groups,  it  is  well  to  begin  with  a  sure  rule  for 
recognizing  them.  Whatever  a  fertilized  egg  produces,  no 
matter  what  it  looks  like,  is  a  sporophyte ;  and  whatever 
a  spore  produces,  no  matter  what  it  looks  like,  is  a  gameto- 
phyte. If  this  rule  is  remembered,  the  two  generations  will 
be  recognized  in  spite  of  all  their  disguises. 

47.   The  Mosses.  —  The  Mosses  are  much  more  abundant 
now  than  the  Liverworts,  and  are  able  to  live  in  much  more 
exposed  places.     In  fact,  Mosses  are  as- 
sociated with  Lichens  in  the  ability  to 
live  in  conditions  that  are  impossible 
for  other  plants.     That  ancient   Liver- 
worts were  the  ancestors  of  Mosses  is 
generally  believed,  and  the  first  question 
is  as  to  the  differences  that  distinguish 
Mosses  from  Liverworts. 

It  will  be  remembered  that  in  some 
Liverworts  the  disk  bearing  the  sex- 
organs  is  lifted  up  from  the  rest  of  the 
body  by  a  long  stalk  (Figs.  53  and  54). 
Since  this  stalk  bears  the  sex-organs 
(which  contain  the  gametes),  it  is  called 
a  gametophore  (" gamete-bearer").  In 
the  Mosses  this  gametophore  always 
appears,  but  instead  of  being  a  naked  stalk,  as  in  Liver- 
worts, it  is  covered  with  numerous  small  leaves  (Fig.  59). 


FIG.  59.  —  The  leafy  gam- 
etophore (leafy  branch) 
of  a  moss  rising  as  a 
branch  from  the  pros- 
trate filamentous  body. 


78 


ELEMENTARY   STUDIES   IN   BOTANY 


The  distinguishing  mark  of  a  moss,  therefore,  is  the 
leafy  gametophore.  It  is  these  leafy  and  usually  branch- 
ing gametophores  that  people  in  general  think  of  as  the 
"  moss  plant,"  for  they  are  the  most  conspicuous  part  of 
it.  It  is  evident  that  green  tissue  in  the  form  of  leaves  on 
a  gametophore  is  in  a  much  better  position  in  reference  to 
air  and  sunlight  than  green  tissue  prostrate  on  some  sub- 


FIG.  60.  —  The  filamentous  body  of  a  young  moss  plant :  A,  the  filament  starting  from 
the  spore  (s)  ;  B,  the  older  filament,  showing  the  branching  habit,  rhizoids  (r),  and 
a  bud  (6)  which  is  to  develop  a  leafy  gametophore.  —  After  MUELLER-THURGAU. 

stratum,  as  in  the  Liverworts.  Since  the  leafy  gameto- 
phore is  only  a  vertical  branch  from  the  prostrate  body,  it  is 
often  called  the  leafy  shoot. 

In  most  Mosses  the  prostrate  (dorsiventral)  body  does 
not  develop  like  those  of  Liverworts,  but  instead  of  being 
a  flat  sheet  of  cells,  it  is  a  green,  branching  filament,  resem- 
bling a  green,  filamentous  Alga  (Fig.  60).  It  is  important  to 
know  that  when  the  liverwort  body  is  developing  it  passes 
through  a  filamentous  stage  before  it  becomes  a  sheet  of  cells. 
This  means  that  the  filamentous  body  of  the  moss  is  not  a 


BRYOPHYTES 


79 


different  kind  of  body,  but 
resembles  a  liverwort  body 
that  has  not  fully  devel- 
oped. This  failure  of  most 
Mosses  to  develop  bodies 
to  the  mature  liverwort 
stage  is  probably  associ- 
ated with  the  fact  that 
the  gametophore  bears 
leaves  and  the  chief  work 
of  food  manufacture  is 
done  no  longer  by  the  pros- 
trate body. 

The  picture  of  a  moss, 
therefore,  is  a  delicate, 
prostrate,  branching,  green 
filament  (which  most  peo- 
ple do  not  see),  from  which 
arise  numerous  vertical 
leafy  branches  (which  most 
people  regard  as  the  whole 
plant),  and  since  these 

leafy  branches  are  gametophores,  they  bear  the  sex-organs. 
There  is  some  excuse  for  regarding  the  branching  gameto- 
phore as  the  whole  plant,  for 
it  sends  out  its  own  rhizoids 
into    the    substratum,    the 
delicate  green  filament  from 
which  it  arose  dies,  and  the 
gametophore  becomes  com- 
pletely    independent     (Fig. 
61).      In  addition   to   this, 
the  gametophore  can  repro- 
duce   extensively    by    vegetative    multiplication,    so    that 
masses  and  "  beds  "  of  moss   are  formed.     In  fact,  most 


FIG.  61.  —  A,  a  leafy  branch  (gametophore) 
that  has  become  independent  by  putting 
out  its  own  rhizoids ;  B,  a  rosette  of 
leaves  surrounding  a  group  of  sex-organs 
(forming  the  so-called  "moss  flower"). 


FIG.  62.  —  Tips  of  leafy  branches  of  a 
moss,  one  of  them  bearing  a  group  of 
sex-organs  surrounded  by  a  rosette  of 
modified 'leaves. 


80 


ELEMENTARY   STUDIES   IN   BOTANY 


of  our  experience  with  Mosses  is  their  occurrence  in  sheets 
and  beds. 

48.  The  sex-organs.  —  It  is  evident  that  the  prostrate 
filamentous  body  of  a  moss  with  its  leafy  gametophore  branch 
is  the  gametophyte  generation.  The  antheridia  and  arche- 


C 


FIG.  63.  —  Sex-organs  of  a  moss:  A,  an  antheridium  discharging  sperms,  one  of  which 
is  shown  (c)  ;  B,  section  of  a  group  of  archegonia  invested  by  leaves :  C,  an  arche- 
gonium,  with  its  long  neck,  and  its  venter  containing  an  egg.  —  After  SACHS. 

gonia  have  the  same  general  structure  as  do  those  of  Liver- 
worts (Fig.  63),  and  are  borne  in  clusters  at  the  tips  of  branches 
or  of  the  main  axis  (Fig.  62).  The  leaves  about  these  ter- 
minal clusters  often  become  close  set,  forming  a  rosette,  and 
they  may  differ  in  appearance  (size  or  color)  from  the  other 


BRYOPHYTES 


81 


leaves  (Figs.  61,  B,  and  62).  These  rosettes  of  leaves  in- 
closing sex-organs  have  been  called  moss  "  flowers/'  but  they 
hold  no  relation  to  real  flowers.  In  a  single  one  of  these 
moss  rosettes  both  kinds  of  sex-organs  (antheridia  and  arche- 
gonia)  may  occur,  or  only  one  kind  (Fig. 
63,  B).  In  the  latter  case,  therefore,  there 
are  male  rosettes  and  female  rosettes ; 
and  if  such  rosettes  occur  on  different 
plants,  there  are  male  plants  and  female 
plants. 

49.  The  sporophyte. — The  sporophyte 
of  a  moss  is  much  more  elaborate  than 
that  of  a  liverwort.     Usually  it  is  long- 
stalked,  the   capsule    (spore-case)    opens 
by  a  lid,  the  spore-bearing  region  is  small 
compared  with  the  rest  of  the  sporophyte, 
and  the  whole  structure  is  very  complex 
(Figs.  64  and  65) ;   but  it  still  lives  as  a 
parasite  on  the  gametophyte,  and  is  com- 
monly (and  wrongly)  called  the  " fruit" 
of  the  moss. 

50.  Evolution    of   the    sporophyte.  - 
After  the  establishment  of  alternation  of 
generations  by  Liverworts,  the  most  im- 
portant  fact  in  connection  with   Bryo- 
phytes  (Liverworts   and  Mosses)   is  the 
progress  made  by  the  sporophyte,  which 
is  usually  spoken  of  as  its  "  evolution." 
It   was   upon  the   sporophyte   that   the 
whole  future  of  the  plant  kingdom  de- 
pended, for  it  is  the  structure  of  the  sporophyte  that  de- 
termines the  higher  groups. 

First  stage  of  the  sporophyte.  —  The  simplest  sporophytes 
among  the  Liverworts  are  merely  spore-cases,  consisting  of 
a  jacket  of  sterile  cells  (cells  that  do  not  produce  spores) 


FIG.  64.  —  Two  moss 
plants  (leafy  gam- 
etophytes)  bearing 
mature  and  long- 
stalked  sporophytes ; 
the  spore-case  on  the 
left  is  still  covered 
by  the  cap  (calyptra) 
formed  by  the  arche- 
gonium;  the  spore- 
case  on  the  right 
shows  the  lid  which 
drops  off  and  ex- 
poses the  spores. 


82 


ELEMENTARY    STUDIES   IN   BOTANY 


investing  a  mass  of  spore-producing  cells  (Fig.  66,  A). 
There  is  no  stalk,  and  there  are  no  sterile  cells  except  the 
single  layer  forming  the  jacket.  When  the  sporophyte 
gets  to  be  very  complex,  it  is  important  to  remember  that  the 
oldest  tissue  in  it  (historically)  is  that  which  produces  spores 
(sporogenous  tissue),  for  this  will  clear  up  many  false  im- 
pressions. 

Progressive  changes.  —  The  conspicuous  change  observed 
in  certain  other  Liverworts  is  that  the  cells  inclosed  by  the 
sterile  jacket  do  not  all  produce  spores.  For  example,  in 

some  forms  one-half  of 
the  inclosed  tissue  pro- 
duces spores  and  the 
other  half  remains  sterile 
(Fig.  66,  B).  This  sterile 
tissue  forms  a  short  stalk, 
and  so  different  regions  of 
the  body  begin. 

In  other  forms,  still 
more  tissue  remains  ster- 
ile, which  means  that  the 
sporogenous  tissue  be- 
comes relatively  less  in 

amount  (Fig.  66,  C).  With  the  increase  of  sterile  tissue,  the 
stalk  and  the  capsule  become  more  complex  (Fig.  66,  D) ; 
until  in  the  higher  Mosses  almost  the  whole  complex  sporo- 
phyte is  sterile,  and  the  sporogenous  tissue  is  not  only 
relatively  small  in  amount,  but  appears  late  in  the  develop- 
ment of  the  sporophyte  (Fig.  66,  E).  The  sporogenous 
tissue  which  in  the  beginning  was  the  first  and  only  tissue 
(except  the  sterile  jacket),  becomes  finally  in  the  higher 
Bryophytes  the  latest  and  most  inconspicuous  part  of  the 
sporophyte.  '  It  is  the  ever  increasing  sterile  tissue  that  the 
higher  plants  use  in  carrying  the  sporophyte  to  still  more 
advanced  stages. 


FIG.  65.  —  Spore-cases  of  a  moss  from  which 
the  lids  have  fallen,  showing  the  teeth. 
—  After  KERNER. 


BRYOPHYTES 


83 


Anthoceros.  —  Among  the  Liverworts  there  is  a  group  of 
which  Anthoceros  may  be  used   as  a  representative.     The 

body  is  a  prostrate 
sheet  of  cells,  some- 
times lobed  but  not 
leafy,  and  resembles 
the  bodies  of  many 
Liverworts  (Fig.  67). 
It  is  not  complex  either 
in  structure  or  in  form, 
but  it  has  a  remark- 
able sporophyte.  It 
is  believed  by  many 
that  this  represents  the 
kind  of  liverwort  spo- 
rophyte that  gave  rise 


B 


FIG.  66.  —  Diagrams  illustrating  the  evolution  of 
the  sporophyte  among  Bryophytes:  A,  sporo- 
phyte of  Riccia,  being  only  a  spore-case ;  B, 
sporophyte  of  Marchantia,  showing  a  reduced 
amount  of  sporogenous  tissue,  and  the  sterile 
cells  forming  a  short  stalk;  C,  sporophyte  of  a 
leafy  Liverwort,  showing  further  reduction  of 
sporogenous  tissue  and  corresponding  increase 
of  sterile  (stalk-forming)  tissue ;  D,  sporophyte 
of  Anthoceros,  showing  further  decrease  of  spo- 
rogenous tissue  and  increasing  complexity  of 
capsule  and  stalk  (including  foot)  ;  E,  sporo- 
phyte of  a  Moss,  showing  extreme  reduction  of 
sporogenous  tissue  and  great  complexity  of  cap- 
sule and  stalk;  the  numerals  (1-1)  indicate  the 
first  wall  of  the  dividing  egg  (note  that  in  A 
and  B  the  two  halves  of  the  egg  contribute 
almost  equally  to  the  sporophyte ;  that  in  C 
one-half  of  the  egg  produces  the  sporophyte ; 
that  in  D  the  first  wall  is  vertical ;  and  that  in 
E  almost  all  the  sporophyte  is  produced  by 
one-half  of  the  egg. 


FIG.  67.  —  Anthoceros:  the  pros- 
trate body  bearing  long  and 
narrow  sporophytes ;  the  two 
sporophytes  to  the  left  are 
mature  and  have  split  to 
discharge  the  spores. 


to    the   higher  groups  of  plants.      If  this  is  true,  such  a 
sporophyte  deserves  special  attention. 

Throughout  the  Bryophytes   (Liverworts    and    Mosses), 


84 


ELEMENTARY   STUDIES   IN   BOTANY 


the  sporophyte  is  dependent  upon  the  gametophyte,  and  is 
never  an  independent  plant.  In  the  higher  groups  (Fern- 
plants  and  Seed-plants)  the  sporophyte  is  an  independent 
leafy  plant.  In  some  way,  the  dependent, 
leafless  sporophyte  of  Bryophytes  becomes 
the  independent,  leafy  sporophyte  of 
Pteridophytes  (Fern-plants),  and  the  liver- 
wort Anthoceros  has  a  sporophyte  that 
has  suggested  the  way.  Just  as  Liver- 
worts are  more  important  than  Mosses 
in  the  history  of  the  plant  kingdom,  so 
are  the  Anthoceros  forms  the  most  im- 
portant Liverworts  in  the  history,  al- 
though they  are  the  least  abundant. 

From  what  has  been  said,  it  is  evident 
that  any  sporophyte  of  the  Bryophytes 
that  shows  a  tendency  to  become  inde- 
pendent is  on  the  way  towards  an  inde- 
pendent sporophyte,  and  when  complete 
independence  is  attained  the  sporophyte 
no  longer  belongs  to  Bryophytes.  The 
peculiarity  of  the  Anthoceros  sporophyte 
is  that  it  is  more  nearly  independent  than 
the  sporophyte  of  any  other  bryophyte. 
This  sporophyte  does  not  consist  of  a 
roundish  spore-case  on  a  more  or  less 
elongated  stalk,  as  in  other  Liverworts 
and  in  the  Mosses,  but  elongates  without 
a  stalk,  until  it  resembles  a  small  grass- 
blade  (Fig.  67).  The  most  striking  fact, 
however,  is  not  its  form,  but  that  it  is  as 
green  as  a  grass-blade.  The  presence  of 
chloroplasts  means  that  this  sporophyte  is  able  to  manu- 
facture food,  and  although  it  has  a  bulbous  foot  sunk  in 
the  thin  body  of  the  gametophyte  (Fig.  68),  it  does  not 


FIG.  68.  —  Anthoceros: 
longitudinal  section 
through  the  sporo- 
phyte (broken  into 
three  regions),  show- 
ing the  bulbous  foot 
imbedded  in  the 
gametophyte,  and 
the  three  regions  of 
the  sporophyte 
above  :  (1)  the  green 
region  (four  layers 
of  cells),  (2)  the 
spore-producing  re- 
gion (the  stages  in 
spore-formation  may 
be  observed  by  trac- 
ing this  region  from 
below  upwards),  and 
(3)  a  central  region. 


BRYOPHYTES  85 

obtain  all  its  food  from  the  gametophyte.  If  such  a  sporo- 
phyte  should  establish  connections  with  the  soil  (on  which 
the  gametophyte  is  lying)  by  means  of  roots,  it  would  be- 
come an  independent  plant,  and  no  longer  be  a  bryophyte. 

Although  the  sporophyte  of  Anthoceros  has  been  likened  to 
a  small  grass-blade  in  form  and  color,  it  is  very  far  from  having 
the  structure  of  a  grass-blade,  for  it  is  in  no  sense  a  leaf.  It 
is  a  stem-like  structure,  which  has  the  power  of  elongating 
like  a  stem,  and  a  section  across  it  shows 
three  regions  (Figs.  68  and  69) ;  (1)  a 
green  region  on  the  outside,  (2)  a  spore- 
producing  region  next  to  the  green,  and 
(3)  a  central  region  of  colorless  and  sterile 
cells.  This  is  the  structure  which  is 
thought  to  have  given  rise  to  sporo- 
phytes  with  stems  and  leaves. 

51.   The  failure  of  Bryophytes.  —  This 

J     r    J  FIG.    69. —  Anthoceros: 

does     not    mean    that    Bryophytes    are         cross-section  of  a  spo- 

,,    .,  •         ,i  i  f          '.  i  rophyte,  showing  the 

failures  in  themselves,  for  it  has  been  three  regions  de- 
seen  that  they  are  abundant  enough  to  esf  t'he  very  distSt 
be  called  successful.  The  failure  referred  sur[ace  l?y*T  °f  ce«« 

is  the  epidermis. 

to  is  that  the  bryophyte  plan  could  not 
make  any  further  progress  leading  to  higher  plants.     We 
infer  that  this  is  true,  simply  because  the  plan  of  the  higher 
plants  is  different. 

A  gametophore  is  developed  by  many  Liverworts  and  by 
all  Mosses.  As  the  name  implies,  this  stalk  carries  up  the 
gametes  (eggs  and  sperms)  above  the  general  surface  of  the 
prostrate  body.  Since  the  fertilized  egg  produces  the  spo- 
rophyte with  its  spore-case,  the  gametophore  certainly  puts 
the  spores  in  a  favorable  position  for  dispersal  by  air.  If 
this  position  favors  the  spores,  however,  it  does  not  favor 
the  sperms  which  must  swim,  for  they  are  carried  up  into  a 
position  of  least  moisture.  It  is  an  interesting  arrangement 
that  favors  spores  by  interfering  with  the  very  act  (fertiliza- 
7 


86  ELEMENTARY    STUDIES   IN   BOTANY 

tion)  that  results  in  spores ;  but  it  works  reasonably  well  for 
plants  living  in  moist  situations. 

The  Mosses  use  the  upright  gametophore  for  the  display 
of  green  tissue,  and  it  becomes  leafy ;  but  the  larger  and  more 
exposed  the  gametophores  of  Mosses  become,  the  more  un- 
likely it  is  that  fertilization  can  occur.  It  is  evident  that 
still  larger  and  more  leafy  plants  would  interfere  with  the 
swimming  of  sperms  still  more. 

The  three  things  that  enter  into  this  problem  are  food 
manufacture  (which  means  display  of  green  tissue  to  light 
and  air),  fertilization  (which  means  water  for  swimming), 
and  spore-production  (which  means  exposure  for  air-disper- 
sal). •  In  the  Bryophytes,  food  manufacture  and  fertilization 
belong  to  the  gametophyte,  and  the  condition  that  favors 
one  hinders  the  other.  In  other  words,  they  are  contradic- 
tory in  their  demands.  On  the  other  hand,  food  manufac- 
ture and  spore-dispersal  make  the  same  demands  for  exposure, 
and  therefore  they  can  be  coupled  together  to  advantage. 
The  further  progress  of  plants,  therefore,  demanded  that  the 
spore-producing  generation  (sporophyte)  should  also  become 
the  food-manufacturing  generation;  and  that  the  gameto- 
phyte, with  its  peculiar  need  for  free  water,  should  be  re- 
stricted to  fertilization.  In  the  higher  plants  (Fern-plants 
and  Seed-plants),  therefore,  the  sporophyte  is  the  conspicuous, 
leafy,  independent  generation,  and  the  gametophyte  is  so 
very  inconspicuous  that  it  is  only  seen  by  those  who  know 
where  and  how  to  look. 

52.  Summary.  —  The  contribution  of  the  Bryophytes 
to  the  progress  of  the  plant  kingdom  is  notable.  Of  first 
importance  is  the  establishment  of  the  land  habit  by  green 
plants  (Liverworts),  which  means  exposure  to  air  rather  than 
to  water7~7This  made  possible  the  further  development  of 
plants  on  the  land  surface.  In  consequence  of  this  change 
in  conditions  of  living,  the  plant  bodies  are  much  more  com- 
pact, and  develop  protective  structures  against  excessive 


BRYOPHYTES  87 

loss  of  water  by  evaporation.  Not  only  are  the  working 
bodies  protected,  but  the  sexual-cells  are  jacketed,  so  that 
the  sex-organs  (antheridium  and  archegonium)  are  many- 
celled.  ^ 

The  most  significant  result  of  the  land  habit  was  the  es- 
tablishment of  an  alternation  of  generations,  so  that  sporo- 
phyte  and  gametophyte  alternate  regularly  in  the  life-history. 
Among  Bryophytes  the  gametophyte  is  the  conspicuous 
generation,  because  it  manufactures  food  in  addition  to  pro- 
ducing sex-organs,  and  the  sporophyte  is  dependent  upon  it. 
In  one  group  of  Bryophytes  (Anthoceros)  the  sporophyte  is 
green,  so  that  the  possibility  of  an  independent  sporophyte  is 
evident. 

The  further  progress  of  the  plant  kingdom  is  dependent 
upon  an  independent  sporophyte,  because  the  free  display  of 
green  tissue  by  a  gametophyte  means  conditions  unfavorable 
for  the  swimming  of  sperms  necessary  to  fertilization,  while 
the  free  display  of  green  tissue  by  a  sporophyte  means  con- 
ditions favorable  also  for  the  dispersal  of  spores. 


CHAPTER  VI 
PTERIDOPHYTES 

THE  FIRST  VASCULAR  PLANTS 

53.  Recapitulation.  —  The  history  of  the  plant  kingdom 
has  been  followed  from  the  Algae,  exposed  to  water,  to  the 
Liverworts,  exposed  to  air.  From  the  Algse  the  dependent 
Fungi  seem  to  have  come,  and  together  the  two  groups  con- 
stitute the  Thallophytes,  the  lowest  great  division  of  plants. 
From  the  Algse  the  Liverworts  also  came  by  acquiring  the 
land  habit,  and  in  turn  gave  rise  to  Mosses,  and  Liverworts 
and  Mosses  together  constitute  the  Bryophytes,  the  second 
great  division  of  plants.  In  the  Bryophytes  the  body  is  more 
complex  than  in  the  Thallophytes,  is  related  to  air  exposure, 
and  alternation  of  generations  is  established.  In  this  alter- 
nation the  gametophyte  is  the  independent  generation,  dis- 
playing the  green  tissue  and  bearing  the  sex-organs ;  and  the 
sporophyte  is  a  dependent  generation.  In  such  Liverworts 
as  Anthoceros,  however,  the  dependent  sporophyte  has  ad- 
vanced far  towards  independence,  as  shown  by  its  develop- 
ment of  abundant  green  tissue,  which  makes  the  sporophyte 
only  partially  dependent.  Therefore,  it  seems  probable  that 
the  Liverworts  gave  rise  not  only  to  the  Mosses,  but  also  to 
the  third  great  division  of  plants  (Pteridophytes),  with  its 
completely  independent  sporophyte.  It  is  important,  there- 
fore, to  examine  the  structure  of  the  independent  sporophyte, 
for  it  involves  much  more  than  the  appearance  of  green 
tissue. 

88 


PTERIDOPHYTES  89 

54.  The  vascular  system.  —  In   all   independent  sporo- 
phytes  there  develops  a  tissue  which  does  not  appear  in  the 
dependent  sporophytes  of  Bryophytes.     It  is  called  vascular 
tissue,    which   means   a   tissue   composed   of   vessels.     The 
so-called  vessels  are  thick-walled,  tubular  cells  that  extend 
through  the  sporophyte  and  are  equipped  to  conduct  water. 
The  vascular  tissue  does  more  than  conduct  water,  but  its 
other  work  will  be  considered  later.     Of  course  water  is 
conducted  through  the  bodies  of  Liverworts  and  Mosses, 
but  the  vascular  tissue  conducts  it  with  more  rapidity  and 
precision  than  any  other  tissue.     The  difference  between 
water-conduction  in  a  liverwort  and  in  a  plant  with  vascular 
tissue  may  be  likened  to  the  difference  between  water  work- 
ing its  way  through  a  swamp  and  water  moving  in  definite 
channels. 

It  must  not  be  supposed  that  the  water-conducting  vessels 
are  continuously  open  tubes,  as  are  the  arteries  and  veins  of 
the  human  body  or  the  water  pipes  of  a  house.  They  are 
elongated  cells  set  end  to  end,  so  that  water  in  moving  through 
the  tissue  must  pass  through  numerous  cell-walls,  thousands 
of  them  in  an  ordinary  stem.  How  water  moves  under  these 
conditions  is  not  known  with  certainty,  but  the  direction  of 
its  movement  is  clear. 

The  vascular  tissue  does  not  extend  at  random  through  the 
body  of  the  sporophyte,  but  has  a  definite  organization,  so 
that  there  is  a  vascular  system  in  every  sporophyte.  The 
vascular  system  has  proved  to  be  of  very  great  service  in  the 
study  of  the  relationships  of  vascular  plants,  for  it  differs 
in  the  various  great  groups.  That  part  of  the  vascular  tissue 
which  conducts  water  is  called  the  xylem,  which  means. 
"  wood,"  for  the  ordinary  wood  of  trees  is  xylem  tissue. 

55.  The  leaf.  —  In   addition   to  a  vascular  system,  the 
independent  sporophyte  has  leaves.     Leaves  are  simply  ex- 
pansions of  green  tissue  that  increase  the  amount  of  green 
tissue  exposed,  and  so  increase  the  capacity  of  the  plant  for 


90  ELEMENTARY   STUDIES   IN   BOTANY 

food-manufacture.  It  must  not  be  supposed  that  leaves  do 
all  the  work  of  food-manufacture,  for  it  is  done  by  any  green 
part  of  the  plant ;  but  leaves  do  the  most  of  it  because  they 
display  the  most  green  tissue. 

The  leaves  of  leafy  Liverworts  and  of  Mosses  have  been 
spoken  of,  but  those  leaves  belong  to  the  gametophyte.     It 


FIG.  70.  —  Portion  of  the  leaf  of  a  maidenhair  fern  (Adiantum),  showing  the  forking 

veins.  • 

is  in  vascular  plants  that  one  meets  the  first  sporophyte 
leaves ;  and  they  are  very  different  in  structure  from  gameto- 
phyte leaves. 

An  important  fact  to  observe  in  connection  with  the  leaves 
of  vascular  plants  is  that  they  are  not  merely  expansions  of 
green  tissue,  but  that  through  the  green  tissue  there  extend 
"  veins  "  (Fig.  70).  These  so-called  veins  are  extensions  of 
the  vascular  system  into  the  leaf,  for  the  xylem  carries  water 


PTERIDOPHYTES 


91 


to  the  working  cells.     Leaves  differ  in  the  arrangement  of 
their  veins,  but  every  arrangement  means  an  effective  dis- 
tribution of  water  to  the  working  cells.     There  are  main 
veins  (often  only  one)  that  give  rise  to  smaller  ones,  and  these 
in  turn  to  still  smaller  ones,  until  the  system  of  veins  forms 
a     complete     network 
through  the  green  tissue 
(Fig.  155).    The  system 
may  be  likened  to  the 
water-pipe  system  of  a 
house,    with    its    main 
pipe,    which    gives    off 
smaller  pipes,  and  these 
in    turn    still     smaller 
ones,  until  every  room 
in  a  large  house  may  be 
supplied  with  water. 
/    The   vein   system  of 
/  a   leaf,   in   addition  to 
/  carrying    water,     inci- 
dentally  forms    a   stiff 
framework    with     its 
woody     fibers,     which 
helps    to    support    the 
I      delicate     green     tissue 
and  keep  it  from  col- 
lapsing. 

It  is  known  to  every 
one  that  leaves  are  ex- 
tremely variable  in  size 
and  form.      For  exam- 
ple, among  the  Pteridophytes,  the  first  great  group  of  vas- 
cular plants,  they  are  very  small  in  the  Club-mosses  (Fig. 
71),  and  are  often  very  large  among  the  Ferns  (Fig.  72). 
Also  in  the  Club-mosses  the  whole  leaf  is  a  single  small  blade 


FIG.  71.  —  Branch  of  a  club-moss  (Selaginella,), 
showing  the  numerous  simple  leaves;  the 
leaves  at  the  tips  of  the  branches  bear  spo- 
rangia, and  therefore  are  sporophylls,  so  that 
each  branch-tip  in  this  case  is  a  strobilus. 


92 


ELEMENTARY   STUDIES   IN   BOTANY 


(as  the  green  expansion  is  called),  while  in  many  Ferns  the 
large  leaf  may  be  broken  up  into  many  blades  (Figs.  70 
and  72). 

Since  the  largest  amount  of  working  tissue  is  exposed  to 
the  air  by  leaves,  it  follows  that  the  leaves  lose  most  water. 


(FIG.  72.  —  Shield  ferns  (Aspidium),  showing  the  large  leaves  broken  into  many  blades. 

They  must  be  kept  full  of  water  and  they  must  be  exposed 
to  the  air,  so  that  great  loss  is  inevitable,  and  the  vascular 
system  must  make  it  good.  The  escape  of  water  from  plants, 
chiefly  by  way  of  the  leaves,  is  called  transpiration,  but  it 
might  just  as  well  be  called  plant-evaporation,  for  the  water 
evaporates  from  the  moist  cells  of  the  plant  just  as  it  does 
from  any  moist  surface  exposed  to  the  air.  How  the  leaves 


PTERIDOPHYTES  93 

are  constructed  so  that  the  loss  of  water  may  not  be  greater 
than  the  supply  will  be  considered  later. 

56.  The  stem.  —  An  independent  sporophyte  has  not 
only  a  vascular  system  and  leaves,  but  also  a  stem ;  in  fact, 
the  presence  of  leaves  implies  a  stem  to  bear  them.  The  most 
important  fact  about  a  stem  is  that  it  bears  leaves  and  exposes 
them  to  the  air  and  the  sunlight.  In  proportion  as  stems  be- 
come taller,  the  better  are  the  leaves  exposed  ;  and  in  propor- 


FIG.  73.  —  Cross-section  of  the  central  cylinder  of  the  stem  (rootstock)  of  a  fern ;   the 
cylinder  is  solid,  the  large  water-conducting  vessels  (xylem)  being  at  the  center. 

tion  as  the  stems  become  branched,  more  leaves  can  be  pro- 
duced and  exposed. 

As  the  stems  carry  the  leaves  up  into  the  air  and  sunlight, 
they  must  also  supply  them  with  water,  and  this  means  that 
the  vascular  system  of  the  stem  must  connect  with  the  vas- 
cular system  (vein  system)  of  the  leaves.  In  the  stem  the 
vascular  system  is  organized  as  a  central  cylindei^so  that  it 
is  called  the  vascular  cylinder  (Figs.  73  anoT74)7  This  cyl- 
inder not  only  conducts  water,  but  also  gives  rigidity  to  the 


94 


ELEMENTARY    STUDIES   IN   BOTANY 


stem,  so  that  in  most  cases  it  stands  upright.  The  move-^ 
ment  of  water  up  the  stem,  through  the  vascular  cylinder,  is 
commonly  spoken  of  as  the  "  ascent  of  sap,"  the  "  sap 
being  water  on  its  way  to  the  leaves. 

It  must  not  be  supposed  that  all  stems  are  upright,  for  in 
many  Olub-mosses  they  are  prostrate,  but  as  they  elongate 
they  produce  and  display  many  leaves.  Nor  must  it  be  sup- 
posed that  all  stems  are 
above  ground,  for  in  the 
most  common  Ferns  the 
stem  is  underground,  but 
it  sends  its  leaves  above 
ground.  These  under- 
ground stems  are  usually 
mistaken  for  roots,  but 
they  can  always  be  recog- 
nized as  stems  by  the/ 
fact  that  they  produce/ 
leaves  and  by  the  kind 
of  vascular  cylinder  they 
possess. 

57.  The  root.  --An 
independent  sporophyte 
has  not  only  a  vascular 
system,  leaves,  and  a  stem,  but  also  roots.  The  leaves 
need  water,  which  the  stem  supplies,  but  roots  must  receive 
water  from  the  soil  and  supply  it  to  the  stem.  Thus, 
the  vascular  system  is  a  water-conducting  system  connecting 
the  roots  with  the  leaves,  through  the  stem.  No  one  of  the 
four  structures  mentioned  as  belonging  to  an  independent 
sporophyte  is  independent  of  the  others.  The  presence  of 
leaves  implies  a  vascular  system,  a  stem,  arid  a  root ;  and 
so  for  each  structure  in  turn.  They  all  belong  together  as 
parts  of  one  machine.  How  the  roots  receive  water  from 
the  soil  will  be  considered  later. 


FIG.  74.  —  Cross-section  of  the  central  cylinder 
of  the  stem  of  a  fern ;  the  water-conduct- 
ing vessels  form  a  hollow  cylinder  inclosing 
pith. 


PTERIDOPHYTES 


95 


Roots  not  only  receive  water,  but  they  also  anchor  the  I 
plant  in  the  soil,  so  that  the  grip  of  the  roots  and  the  rigidity ' 
of  the  stem  hold  the  plant  firmly  in  place. 


FIG.  75.  —  A  club-moss  (Lycopodium)  :  A,  the  whole  plant,  showing  the  horizontal 
and  very  leafy  stem  giving  rise  to  roots  and  erect  branches  bearing  very  distinct 
strobili  (composed  of  sporophylls)  ;  B,  a  single  sporophyll  with  its  sporangium ; 
C,  spores  much  magnified.  —  After  WOSSIDLO. 

The  root  differs  very  much  from  the  stem  in  structure,  and 
especially  is  it  different  in  its  vascular  cylinder,  and  in  the 


96 


ELEMENTARY    STUDIES   IN    BOTANY 


fact  that  it  does  not  produce  leaves.  Like  the  stem,  it  often 
branches,  and  this  means  a  greater  capacity  for  receiving 
water.  It  must  not  be  supposed  that  all  roots  are  in  the  soil, 
for  some  roots  are  produced  in  the  air  by  climbing  stems,  and 
anchor  the  stems  to  supports.  In  this  case  they  simply  act 
as  holdfasts  and  do  not  receive  water,  but  they  can  be  recog- 


FIG.  76.  —  Under  surface  of  fern  leaves,  showing  sori :   A,  elongated  sori ;   B,  round  sori. 

nized  as  roots  by  the  vascular  cylinder  and  by  the  fact  that 
they  do  not  bear  leaves. 

58.  The  sporangia.  —  A  sporophyte,  whether  dependent 
or  independent,  must  bear  spores,  and  these  spores  must  be 
placed  in  a  favorable  position  for  dispersal  by  air.  In  the 
dependent  sporophyte  of  Bryophytes,  the  conspicuous  part 


PTERIDOPHYTES 


97 


of  the  body  is  a  spore-case,  and  all  the  spores  are  produced 
in  one  continuous  mass.  In  the  independent  sporophyte  of 
Pteridophytes,  however,  the  root,  stem,  and  leaves  are  the 
conspicuous  structures;  and  if  the  spores  are  to  be  formed 
in  the  most  exposed  position  it  is  evident  that  they  should 
appear  in  connection  with  the  leaves.  Therefore,  among 
Pteridophytes  the  spore-cases  (sporangia)  are  produced  by 


FIG.  77.  —  Section  through  a  sorus  of  a  shield  fern,  showing  the  group  of  sporangia 
covered  by  a  shield-like  (or  umbrella-like)  flap.  —  After  ENQLER  and  PRANTL. 

leaves,  in  some  plants  by  all  the  leaves,  in  other  plants  only 
by  certain  leaves. 

In  the  Club-mosses,  with  their  small  leaves,  a  single  spo- 
rangium is  produced  on  the  upper  surfaco  of  the  leaf  near  its 
base  (Fig.  75).  In  some  of  the  Club-mosses  every  leaf  has 
a  sporangium ;  but  in  most  of  them  only  the  uppermost 
leaves  have  sporangia  (Fig.  75).  In  the  latter  case,  there 
are  two  kinds  of  leaves  on  the  plant ;  (l)  those  that  bear 
sporangia,  and  (2)  those  that  do  not.  The  former  are  called 
sporophylls  ("  spore-leaves  ")>  and  the  latter  foliage  leaves 
(which  means  ordinary  green  leaves). 


98 


ELEMENTARY   STUDIES   IN   BOTANY 


In  the  Ferns,  with  their  relatively  few  and  large  leaves,  the 
sporangia  are  borne  in  large  numbers  on  the  under  surface  of 

the  leaf,  and  usually  occur 
in  small  groups  that  look 
like  dark  dots  or  lines 
(Fig.  76),  which  are  often 
called  " fruit-dots,"  but 
of  course  they  are  not 
fruit.  In  some  Ferns  al- 
most all  of  the  leaves  bear 
sporangia,  while  in  other 
Ferns  many  leaves  are 
without  them.  These 
little  groups  of  sporangia 
are  called  sori  (singular 
sorus),  and  they  are  very 
characteristic  of  Ferns. 
A  section  through  a  sorus 
is  shown  in  Fig.  77. 

59.  The  gametophyte. 
—  The  sporophyte,  with  its  root,  stem,  leaves,  and  spo- 
rangia, seems  to  most  people  to  be  the  whole  plant.  A  fern 
plant,  as  ordinarily  thought  of,  is  simply 
this  sporophyte,  and  it  is  certainly  a  dis- 
tinct and  independent  individual.  But 
it  bears  no  sex-organs  ;  if  it  did,  it  would 
not  be  a  sporophyte.  The  older  observers 
of  plants  were  puzzled  by  the  absence  of 
sex-organs  in  Ferns  and  Club-mosses,  but 
they  thought  that  sex-organs  must  be 
present,  although  invisible.  Therefore, 
they  called  the  group  Cryptogams,  which 
means  "  hidden  sex-organs,"  and  since 
Club-mosses  and  Ferns  are  vascular  plants,  the  Pterido- 
phytes  were  first  called  "  Vascular  Cryptogams,"  and  many 


FIG.  78.  —  Gametophytes  of  ferns:  A,  a  game- 
tophyte viewed  from  the  under  side  (against 
the  substratum),  showing  the  rhizoids  and 
sex-organs,  the  archegonia  (whose  projecting 
necks  are  seen)  being  grouped  near  the  notch , 
and  the  antheridia  being  grouped  at  the 
other  end  (in  the  region  of  the  most  con- 
spicuous rhizoids)  ;  B,  a  gametophyte  (under 
surface)  from  one  of  whose  fertilized  eggs 
(within  an  archegonium)  a  young  sporo- 
phyt*  is  developing,  the  root  being  directed 
downward  and  the  leaf  rising  upward 
through  the  notch. 


FIG.  79.  —  Section  of  an 
archegonium  of  a  fern, 
showing  the  free  neck, 
and  the  imbedded 
venter  containing  the 
egg  (the  large  cell). 


PTERIDOPHYTES 


99 


still   use  that  name,   although  the   sex-organs   have   been 
found. 

The  alternation  of  generations  explains  what  was  a  mystery 
to  the  older  botanists.  When  the  spore  of  a  fern  germinates, 
it  must  produce  a  gametophyte  (see  §  46,  p.  77) .  This  gameto- 
phyte  is  a  minute  green  plant  that  looks  like  a  very  small  and 
delicate  liverwort  (Fig.  78,  A).  In  fact,  it  is  so  small  that 
it  is  only  seen  by  those  who  know  where  to  look  for  it ;  and 


FIG.  80.  —  Antheridia  of  a  fern :  A,  two  antheridia,  one  containing  sperms  and  the  other 
discharging  them  ;  B,  a  single  sperm,  showing  its  coiled  form  and  many  cilia. 

it  does  not  suggest  a  fern  in  the  least.  Although  it  is  flat 
and  prostrate  like  a  liverwort,  unlike  a  liverwort  it  produces 
the  sex-organs  (antheridia  and  archegonia)  from  the  under 
surface,  against  the  moist  substratum  (Figs.  79  and  80). 
This  position  is  very  favorable  for  the  swimming  of  sperms, 
for  if  there  is  moisture  anywhere  about  the  plant,  it  will  be 
found  between  the  flat  body  and  its  substratum.  The  necks 
of  the  archegonia  also  open  on  the  under  surface,  so  that 
fertilization  is  favored  in  every  way. 

The  small  gametophyte  is  large  enough  to  produce  sex- 
organs,  and  it  does  not  make  food  for  the  sporophyte,  so  that 


100 


ELEMENTARY    STUDIES   IN   BOTANY 


great  exposure  to  drying  out  is  avoided,  and  fertilization  is 

assured. 

When  the  fertilized  egg  in  the  archegonium  germinates, 

it  produces  the  large, 
independent  sporo- 
phyte  which  is  recog- 
nized as  "  the  fern  " 
(Fig.  78,  B). 

It  may  have  been 
difficult  for  some  to 
think  of  the  spore- 
case  of  a  liverwort  or 
a  moss  as  being  an 
individual  distinct 
from  the  green  plant 
that  bears  it ;  but 
when  in  the  Ferns 
these  two  individuals 
become  entirely  in- 
dependent of  one  an- 
other, the  difficulty 
disappears. 

60.  The  great 
groups  of  Pterido- 
phytes.— The  Pteri- 
dophytes  are  very  an- 

FIG.  81.  —  Equisetum:  showing  the  jointed  and  fluted  cient  plants     for   their 
stem,  the  sheath  of  minute  leaves  at  each  joint, 

strobili    in    various   stages  of   development,  and  history     has     been 
some  young  branches.  -,      -,        -,  ,-, 

traced    back    to    the 

time  when  coal  was  formed,  and  even  before  that  time. 
Their  remains  are  found  in  the  rocks,  and  this  record  of 
their  existence  has  shown  not  only  that  they  were  very 
abundant,  but .  also  that  they  were  different  from  the 
Pteridophytes  that  are  living  to-day.  A  number  of  great 
groups  lived  and  flourished  and  then  disappeared,  but  they 


PTERlDOtfHYTES 


101 


produced  descendants,  and  among  these  descendants  are  the 
Pteridophytes  of  the  present  time.  The  history  and  fate 
of  these  ancient  groups  may  be  likened  to  the  history  and 
fate  of  such  old  empires 
as  those  of  Egypt,  Greece, 
and  Rome,  which  lived 
and  flourished  and  then 
disappeared,  but  they 
also  gave  rise  to  descend- 
ants, and  among  these 
descendants  are  various 
nations  of  the  present 
time. 

There  are  three  promi- 
nent groups  of  Pterido- 
phytes living  to-day,  and 
they  are  common  enough 
to  deserve  recognition. 

(1)  Club-mosses  (Ly- 
copodiales) . — These 
plants,  resembling  coarse 
mosses,  are  recognized 
by  their  numerous  small 
leaves  (Figs.  71  and  75), 
and  by  the  fact  that  the 
sporangium-bearing 
leaves  (sporophylls)  bear 
a  single  sporangium  upon 
the  upper  surface  near 
the  base.  They  are 
sometimes  called 
"ground  pines,"  because 
the  coarser  ones  resemble  seedling  pines  in  general  appear- 
ance. Among  the  ancestors  of  the  present  Lycopodiales 
there  were  large  trees,  so  that  during  the  Coal  Age  the 
8 


FIG.  82.  —  A  branching  Equisetum. 


102  EH^ARY   STUDIES   IN   BOTANY 


Lycopodiales  were  conspicuous  members  of  the  forests.  At 
present,  however,  they  are  all  small  and  mostly  prostrate 
plants  that  send  up  vertical  branches  bearing  the  sporangia. 

(2)  Horsetails  (Equisetales).  —  These  plants  are  sometimes 
called  "  scouring  rushes,"  and  are  so  peculiar  in  appearance 
that  they  can  never  be  mistaken.  The  stems  are  green  and 
jointed,  and  often  the  joints  can  be  pulled  apart  easily  (Fig. 
81).  At  each  joint  there  is  a  circle  of  minute  leaves  forming 


PIG.  83.  —  Young  fern  leaves  arising  from  the  subterranean  stem  (rootstock),  and  show- 
ing the  rolled  tip. 


a  toothed  sheath,  but  they  are  not  foliage  leaves,  for  they  do 
not  display  green  tissue.  As  a  consequence,  the  stem  looks 
bare,  which  is  especially  noticeable  when  it  does  not  branch. 
When  branching  occurs,  it  may  be  very  profuse,  so  that  the 
plant  looks  like  a  miniature  bush  (Fig.  82).  Since  there  are 
no  foliage  leaves,  all  the  work  of  food  manufacture  must  be 
•done  by  the  green  tissue  of  the  stem. 

The  Equisetums  (which  seems  to  be  a  better  name  to  use 


103 


104  ELEMENTARY   STUDIES   IN   BOTANY 

than  horsetails)  also  have  forest  trees  among  their  ancestors 
of  the  Coal  Age,  and  the  appearance  of  these  conspicuously 
jointed  trees  would  have  been  very  peculiar  to  one  familiar 
only  with  trees  of  the  present  day.  Many  of  the  ancient 
representatives  of  the  group  had  foliage  leaves,  and  in  some 
cases  large  ones,  so  that  the  living  Equisetums  are  rather 
poor  representatives  of  the  group. 

(3)  Ferns  (Filicales) .  —  These  are  the  most  abundant 
and  best  known  of  the  Pteridophytes,  and  hardly  need  a 
definition.  Compared  with  Club-mosses,  Ferns  have  large 
and  relatively  few  leaves,  which  bear  numerous  sporangia 
upon  the  under  surface.  Not  only  are  the  leaves  large,  but 
sometimes  they  become  very  large  by  branching.  It  is  not 
by  its  form  that  a  fern  leaf  can  be  distinguished  from  other 
leaves,  but  by  its  forking  veins  (Fig.  70),  and  by  the  fact  that 
it  first  appears  as  if  rolled  up  from  the  tip  to  the  base,  and 
then  it  expands  by  unrolling  (Fig.  83).  The  leaves  of  Ferns 
were  once  called  "  fronds,"  because  they  were  thought  to  be 
different  from  leaves.  It  was  observed  that  they  came  di- 
rectly from  the  ground,  arising  from  an  underground  struc- 
ture that  was  thought  to  be  a  root  (Fig.  83) .  Therefore,  the 
leaf-like  structure  was  thought  to  be  a  combination  of  stem 
and  leaf,  to  which  the  name  "  frond  "  was  given.  Of  course 
a  fern  leaf  is  not  a  frond,  as  the  underground  structure  re- 
ferred to  is  a  stem  and  not  a  root,  but  many  still  call  it  a  frond. 

The  Ferns  of  ordinary  experience  are  tufts  of  leaves  arising 
from  an  underground  stem  (Fig.  72),  which  also  sends  out 
roots  ;  but  there  are  many  tree  Ferns  in  the  tropics,  the  un- 
branching  trunk  (often  tall  and  slender)  bearing  a  crown  of 
large  and  branching  leaves  (Fig.  84) ;  and  there  are  climbing 
Ferns  in  our  own  eastern  mountain  region;  and  numerous 
perching  Ferns  occur  in  the  tropics,  often  covering  the  trunks 
and  branches  of  trees  (Figs.  85  and  86). 

61.  The  strobilus.  —  This  word  means  "  cone,"  and  its 
use  here  refers  to  the  fact  that  in  some  Pteridophytes  the 


FIG.  85.  —  Perching  ferns  (with  hanging  leaves)  on  a  tree  in  Mexico.  —  Photograph  by 

LAND. 


105 


105  ELEMENTARY    STUDIES   IN   BOTANY 


FIG.  86.  —  A  large  staghorn  fern  perching  on  a  tree  in  Australia.  —  Photograph  by 

CHAMBERLAIN. 

sporophylls  (see  §  58,  p.  97)  become  different  in  appearance 
from  the  foliage  leaves  (usually  smaller,  and  often  different  in 
form),  and  are  grouped  close  together  in  the  form  of  a  cyl- 
inder or  cone  (as  in  the  pine  cone).  This  group  or  cone  of 


PTERIDOPHYTES 


107 


sporophylls  is  the  strobilus  (Figs.  75  and  81),  and  it  is  a  very 
important  structure,  for  it  is  the  precursor  of  the  flower. 

In  general,  the  Club-mosses  have  strobili  very  distinct  from 
the  rest  of  the  body  (Fig.  75),  for  they  are  borne  at  the  ends 
of  the  vertical  branches,  and  are  often  stalked  far  above  the 
foliage-bearing  part   of   the   stems.      It  is 
these  strobili  that  are  the  " clubs"  of  the 
Club-mosses,  a  name  which  may  now  be 
interpreted    as    meaning   moss-like   plants 
that  bear  clubs.     It  must  be  kept  in  mind 
that  in  these  strobili  of  Club-mosses,  each 
sporophyll  bears  a  single  large  sporangium 
on  its  upper  surface  near   the  base,   and 
that  a  strobilus  is  simply  the  tip  of  a  stem 
(or   branch)  bearing   sporophylls   so   close 
together  that  they  overlap. 

The  Equisetums  also  have  strobili  (Fig. 


FIG.  87.  —  Equisetum:  A,  a  single  sporophyll,  showing  the 
peltate  top  from  which  the  sporangia  hang;  B  and  C, 
spores  showing  the  unwinding  of  the  peculiar  bands  that 
form  the  outer  coat. 


FIG.  88.—  Ophio- 
glossum  (adder's 
tongue) :  a  fern 
with  a  part  of 
the  leaf  bearing 
sporangia. 


81),  and  the  sporophylls  are  very  different  from  those  of  the 
Club-mosses,  for  each  sporophyll  is  a  stalk-like  structure 
with  an  expanded  top  ("  peltate  "),  from  the  under  side  of 
which  several  sporangia  are  suspended  (Fig.  87). 

The  Ferns  do  not  have  strobili,  although  in  some  of  them 
there  are  sporophylls  distinct  from  foliage  leaves,  and  in  more 


108 


ELEMENTARY   STUDIES   IN   BOTANY 


of  them  certain  branches  of  the  leaf  bear  sporangia  and  differ 
very  much  in  appearance  from  the  foliage  branches  (Fig. 

88).  But  in  no  case 
are  sporophylls  grouped 
together  to  form  strobili. 

62.  Heterospory.  - 
In  most  of  the  Pterido- 
phytes,  all  the  spores 
produced  by  the  spo- 
rangia are  alike,  both  in 
appearance  and  in  the 
gametophytes  they  pro- 
duce. This  condition  is 
called  homospory  ("  simi- 
lar spores "),  and  such 
plants  are  homosporous. 
In  some  Pterido- 
phytes,  however,  notably 
one  kind  of  club-moss 
(Selaginella,  Fig.  71),  the 
spores  are  not  all  alike 
(Fig.  89).  They  differ 
very  much  in  size,  the 
large  ones  being  called 

FIG.  89.  —  Selaginella  (a  club-moss) :   A,  a  spo-  t    megdSpOreS      ("  large 


rophyll  (microsporophyll)  bearing  the  spo- 
rangium (microsporangium)  that  produces 
small  spores  (microspores)  ;  B,  microspores 
(lowest  one  separate,  upper  ones  clinging 
together)  ;  C,  a  sporophyll  (megasporophyll) 
bearing  the  sporangium  (megasporangium) 
that  produces  large  spores  (megaspores)  ; 
D,  two  megaspores,  drawn  to  the  same  scale 
as  the  microspores  (B). 


spores  ")  and  the  small 
ones  microspores  ("small 
spores").  Not  only  do 
they  differ  in  size,  but 
they  differ  also  in  the 
gametophytes  they  pro- 
duce, the  megaspores  producing  female  gametophytes  (that 
is,  gametophytes  that  bear  only  archegonia),  and  the 
microspores  producing  male  gametophytes  (that  is,  gameto- 
phytes that  bear  only  antheridia).  This  condition  is  called 


PTERIDOPHYTES  109 

heterospory  ("  different  spores "),  and  such  plants  are 
heterosporous. 

Heterospory  is  extremely  important,  for  it  is  the  condition 
that  leads  to  seed-formation ;  that  is,  heterospory  is  the  pre- 
cursor of  the  seed.  Pteridophytes  in  general  are  not  heter- 
osporous, but  heterospory  began  among  Pteridophytes,  and 
when  it  reached  the  formation  of  seeds,  then  Seed-plants 
(Spermatophytes)  began. 

Not  only  are  the  spores  of  heterosporous  plants  different, 
but  the  two  kinds  are  produced  by  different  sporangia  (Fig. 
89).  Therefore  the  sporangia  that  produce  megaspores  are 
called  megasporangia,  and  those  that  produce  microspores 
are  called  microsporangia.  In  Selaginella  (the  heterosporous 
Club-mosses)  the  megasporangia  are  usually  in  the  lower 
part  of  the  strobilus,  and  the  microsporangia  in  the  upper 
part.  The  difference  in  the  size  of  the  spores  involves  a 
difference  in  the  number  of  spores  produced  by  the  two  kinds 
of  sporangia.  In  Selaginella,  for  example,  a  megasporan- 
gium  usually  contains  four  megaspores,  while  a  microspo- 
rangium  contains  hundreds  of  microspores.  Since  the  two 
kinds  of  sporangia  are  approximately  of  the  same  size,  this 
difference  in  the  number  of  spores  will  give  some  idea  of 
their  difference  in  size  (Fig.  89). 

It  is  necessary  also  to  recognize  the  fact  that  the  sporo- 
phylls  that  produce  the  two  kinds  of  sporangia  may  become 
different ;  in  fact,  among  the  Seed-plants  they  become  very 
different.  In  order  to  distinguish  them,  the  sporophylls 
producing  megasporangia  are  called  megasporophylls ;  while 
those  producing  microsporangia  are  called  microsporophylls. 

A  little  experience  with  these  terms  will  make  them  recall 
easily  the  structures  they  stand  for,  especially  if  their  rela- 
tions are  remembered  as  follows  :  a  megasporophyll  bears  one 
or  more  megasporangia,  which  contain  megaspores;  and 
when  megaspores  germinate,  they  produce  female  gameto- 
phytes,  that  is,  gametophytes  that  bear  only  archegonia 


110  ELEMENTARY    STUDIES   IN   BOTANY 

(which  contain  the  eggs) ;  a  microsporophyll  bears  one  or 
more  microsporangia,  which  contain  microspores ;  and  when 
microspores  germinate,  they  produce  male  gametophytes, 
that  is,  gametophytes  that  bear  only  antheridia  (which 
contain  the  sperms). 

It  may  help  to  remember  what  heterospory  involves  in  the 
life-history  of  a  plant  by  giving  the  formula  of  the  life-history 
of  a  heterosporous  plant,  which  of  course  must  include  two 
gametophytes.  The  sexual  cells  (egg  and  sperm)  are  indi- 
cated by  the  conventional  sex  signs  (  ?  is  for  female,  and  $  for 
male),  and  the  two  kinds  of  spores  are  indicated  by  their 
relative  size. 


G-9   x 

,*>- 
G— <? 


S 


Among  the  Seed-plants  it  often  happens  that  the  mega- 
spores  and  microspores  are  borne  on  different  sporophytes, 
so  that  in  such  life-histories  two  sporophytes  must  be  in- 
cluded, as  well  as  two  gametophytes.  Two  sporophytes 
would  need  two  eggs,  so  that  the  formula  becomes  somewhat 
complicated,  but  it  gives  some  appreciation  of  the  machinery 
of'  the  higher  plants. 

CN>3.  Gametophytes.  —  In  §  59  (p.  98)  the  gametophyte  of  a 
fernN^vas  described,  which  may  stand  in  a  general  way  for  the 
gametophytes  of  most  Pteridophytes,  for  most  Pteridophytes 
are  homosporous.  These  gametophytes  are  alike  in  usually 
bearing  both  sex-organs,  therefore  they  are  not  male  or  female, 
but  both ;  and  also  they  are  quite  independent  of  the  sporo- 
phyte  which  produced  them  by  means  of  its  spores. 

But  in  heterosporous  plants  there  are  two  kinds  of  game- 
tophytes, and  these  must  be  described  if  one  is  to  understand 
seeds  when  they  appear. 

When  a  microspore  germinates,  there  appears  within  it 
a  small  group  of  cells,  but  the  group  never  grows  so  as  to 


PTERIDOPHYTES 


111 


break  through  the  wall  of  the  microspore  and  develop  a  free 
plant  (Fig.  90).  When  it  is  remembered  that  whatever  a 
microspore  produces  must  be  a  male  gametophyte,  no  matter 
what  it  looks  like,  this  small  group  of  cells  within  the  micro- 
spore  must  be  the  male  gametophyte.  When  the  group  is 
examined,  it  is  discovered  that  there  is  a  single  antheridium, 
with  its  wall  in- 
closing sperm- 
producing  cells. 
This  represents  a 
gametophyte  that 


FIG.  90.  —  Selaginella: 
the  male  gametophyte 
completely  developed 
within  themicrospore ; 
the  group  of  squarish 
cells  with  nuclei  are 
those  that  produce 
sperms.  —  After  Miss 
LYON. 


FIG.  91.  —  Selaginella:  the  female  gametophyte 
within  the  megaspore,  but  having  burst 
through  on  one  side  :  m,  megaspore  wall ;  a, 
archegonium ;  r,  rhizoid. 


has  disappeared  from  ordinary  sight,  and  that  can  be 
discovered  only  by  the  microscope. 

When  a  megaspore  germinates,  there  appears  within  it 
a  much  larger  group  of  cells  than  appears  in  the  microspore 
(Fig.  91),  for  the  megaspore  is  much  larger  than  the  micro- 
spore.  But  even  this  larger  group  of  cells  does  not  free  itself 
from  the  megaspore  wall  and  grow  into  a  free  plant ;  but 
it  does  develop  archegonia,  and  must  be  the  female  gameto- 
phyte. 

In  heterosporous  plants,  therefore,  the  two  gametophytes 


112 


ELEMENTARY    STUDIES    IN    BOTANY 


have  disappeared  from  ordinary  sight,  and  it  is  not  sur- 
prising that  the  large  and  conspicuous  sporophyte  is  thought 
to  be  the  whole  of  the  plant;  it  is  certainly  the  whole  of 
the  plant  in  sight.  To  find  the  gametophytes,  one  must 
look  within  the  microspores  and  megaspores  with  a  micro- 
scope. 

It  is  instructive  to  trace  the  history  of  the  gametophyte 
and  sporophyte  generations  through  the  great  groups  of 
plants.  In  Bryophytes,  the  gametophyte  is  the  conspicu- 
ous individual,  the  sporophyte  being  dependent  upon  it  and 
being  not  much  more  than  a  spore-case.  In  the  Pterido- 
phytes,  the  sporophyte  has  become  the  conspicuous  individual, 

but  in  most  Pterido- 

Bryophytes    Pteridophytes  Spermatophytes 


FIG.  92.  —  Diagram  illustrating  the  advance  of  the 
sporophyte  and  the  decline  of  the  gametophyte 
through  Bryophytes,  Pteridophytes,  and  Sperma- 
tophytes. 


phytes  the 
phyte  is  a  free  and 
independent  individ- 
ual, although  rela- 
tively very  small.  In 
the  heterosporous 
Pteridophytes  and  in 
all  the  Seed-plants, 
the  gametophytes  are 

neither  free  nor  independent,  and  have  disappeared  from 
view  within  the  spores  that  produce  them.  The  accom- 
panying diagram  (Fig.  92)  will  illustrate  the  gradual 
advance  of  the  sporophyte  and  the  gradual  decline  of  the 
gametophyte  through  the  plant  kingdom. 

64.  Summary.  —  The  most,  important  fact  in  connection 
with  the  Pteridophytes  is  the  appearance  of  an  independent 
sporophyte,  which  is  now  the  conspicuous  generation.  With 
the  appearance  of  an  independent  sporophyte  there  are  asso- 
ciated three  structures  not  found  in  the  lower  groups  of  plants : 
the  vascular  system,  the  sporophyte  leaves,  and  the  root. 

A  second  important  fact  is  that  among  the  Pteridophytes 
the  strobilus  appears,  which  is  the  precursor  of  the  flower. 


PTERIDOPHYTES  113 

The  strobilus  is  not  a  feature  of  all  Pteridophytes,  not  appear- 
ing among  the  Ferns,  but  it  is  a  structure  begun  by  the  group. 
A  third  important  fact  is  the  appearance  of  heterospory, 
for  this  is  the  precursor  of  the  seed.  This  means  a  differentia- 
tion of  the  spores  into  two  kinds,  one  kind  (the  smaller  ones) 
producing  the  male  gametophytes,  the  other  kind  (the  larger 
ones)  producing  the  female  gametophytes.  Another  accom- 
paniment of  heterospory  is  that  the  gametophytes  are  de- 
pendent and  so  small  that  they  remain  within  the  spores 
that  produce  them. 


CHAPTER  VII 
SPERMATOPHYTES.  —  1.   GYMNOSPERMS 

THE  FIRST  SEED-PLANTS 

65.  The  great  plant  groups.  —  In  beginning  a  study  of 
the  fourth  great  group  of  plants,  it  is  appropriate  to  fix  in 
mind  the  chief  distinguishing  features  of  all  the  groups. 
The  following  statement  of  contrasts  may  serve  this  purpose. 

Thallophytes.  —  Plants  with  a  thallus  body,  but  no  arche- 
gonia. 

Bryophytes.  —  Plants  with  archegonia,  but  no  vascular 
system. 

Pteridophytes.  —  Plants  with  a  vascular  system,  but  no 
seeds. 

Spermatophytes.  —  Plants  with  seeds. 

Each  of  the  definitions  (except  the  last)  contains  a  positive 
and  a  negative  statement,  the  positive  statement  distinguish- 
ing the  group  from  the  one  below  it  in  rank  (except  the  first), 
and  the  negative  statement  distinguishing  the  group  from 
the  one  above  it  in  rank. 

The  four  great  groups  should  not  only  be  kept  clearly  in 
mind  by  brief  definitions,  such  as  those  given  above,  but  they 
should  also  be  remembered  for  their  chief  contributions  to 
the  progress  of  the  plant  kingdom.  The  most  conspicuous 
contributions  may  be  stated  as  follows. 

Thallophytes.  —  This  group,  as  represented  by  the  Algae, 
stands  for  the  beginnings  of  plant  structures,  and  chiefly 
for  the  evolution  of  the  three  kinds  of  reproduction. 

Bryophytes.  —  This  group,  as  represented  by  the  Liver- 
worts, stands  for  acquiring  the  land  habit  (which  means  air 

114 


SPERMATOPHYTES  115 

as  a  medium),  and  for  establishing  the  alternation  of  genera- 
tions. 

Pteridophytes.  —  This  group  stands  for  the  development 
of  the  vascular  system  (with  its  associated  leaves  and  roots), 
for  the  introduction  of  the  strobilus,  and  for  the  beginning 
of  heterospory. 

Spermatophytes.  —  This  group  stands  for  the  development 
of  the  seed  and  for  the  evolution  of  the  flower. 

66.  The  two  great  groups  of   Seed-plants.  —  The  Seed- 
plants  are  the  most  conspicuous  plants  to-day,  for  they  make 
up  nearly  all  the  vegetation  that  one  sees.     They  are  cer- 
tainly more  important  than  the  other  groups,  not  only  in 
prominence  and  in  numbers,  but  also  in  the  use  made  of 
them.     They  are  so  prominent  and  useful  that  they  were 
once  thought  to  be  the  only  group  worth  studying ;    but  it 
is  known  now  that  Seed-plants  can  be  understood  best  by 
allowing  the  other  groups  to  explain  them. 

The  Seed-plants  have  developed  as  two  great  groups : 
(1)  those  in  which  the  seeds  are  exposed,  and  (2)  those  in  which 
the  seeds  are  inclosed.  The  first  group  is  named  Gymno- 
sperms  ("  naked  seeds"),  and  the  second  is  named  Angio- 
sperms  ("  inclosed  se*eds ").  The  Gymnosperms  are  the 
ancient  Seed-plants,  and  are  now  much  less  numerous  than 
the  more  modern  Angiosperms.  It  is  the  Gymnosperms, 
therefore,  that  developed  the  first  seeds  and  that  must  be 
considered  first. 

67.  The  ancient  Gymnosperms.  —  In  most  ancient  times 
in  which  we  have  plant  records,  when  the  coal  was  being 
formed,  and  there  were  tree  Club-mosses  and  tree  Equise- 
tums,    the    oldest    Gymnosperms    lived.     They   were    very 
abundant,  for  their  leaves  are  found  everywhere  in  the  rocks 
about  the  coal  mines.     The  leaves  resemble  those  of  Ferns 
.so  exactly  that  they  were  thought  to  belong  to  Ferns,  but 
recently  it  was  discovered  that  they  bore  seeds,  and  therefore 
they  are  Gymnosperms.     The  first  Seed-plants,  therefore, 


116  ELEMENTARY    STUDIES   IN   BOTANY 

looked  like  Ferns  bearing  seeds,  and  it  is  believed  that  they 
came  from  very  ancient  Ferns  by  acquiring  the  seed  habit. 

These  fern-like  Gymnosperms  gave  rise  to  other  groups, 
and  these  in  turn  to  still  others,  until  finally  the  Gymno- 
sperms of  to-day  appeared. 

68.  The  modern  Gymnosperms.  —  The  greatest  group 
of  modern  Gymnosperms  is  the  one  to  which  pines,  spruces, 


FIG.  93.  —  A  group  of  Conifers  (mostly  spruces)  along  the  southern  boundary  of  the 
White  River  Forest  Reserve,  Colorado.  —  Photograph  by  LAND. 

hemlocks,  cedars,  etc.,  belong  (Fig.  93),  and  is  called  Conifers 
("  cone-bearers  ")  on  account  of  the  cones  the  plants  (usually 
trees)  bear.  These  Conifers  are  found  in  forest  masses, 
sometimes  very  extensive,  throughout  the  north  temperate 
regions,  and  they  extend  farther  south  along  the  mountain 
ranges.  Many  of  them  are  extremely  valuable  for  timber, 
and  it  is  well  known  how  extensively  and  ruthlessly  they  have 
been  destroyed  by  man.  In  the  temperate  regions  of  the 
southern  hemisphere  there  is  also  a  great  display  of  Conifers 
that  differ  from  those  of  the  northern  hemisphere. 


SPERMATOPHYTES 


117 


Scattered  through  the  broad  tropical  belt  between  the 
two  temperate  regions   there  is  another  group  of  modern 


FIG.  94.  —  A  Mexican  Cycad  (Dioon  edule).  —  Photograph  by  CHAMBERLAIN. 

Gymnosperms,  called   Cycads.     They  resemble  tree  ferns, 
with  their  columnar  trunks  bearing  crowns  of  large  fern-like 


118  ELEMENTARY   STUDIES   IN   BOTANY 

leaves  (Fig.  94).  Sometimes  the  trunks  are  short,  resem- 
bling casks  or  large  tubers,  but  they  always  bear  the  crown 
of  fern-like  leaves. 

There  are  two  other  living  groups,  very  much  scattered, 
and  very  few  in  numbers,  so  that  they  need  not  be  described. 

The  pine  will  be  used  as  a  representative  of  Gymnosperms, 
since  it  is  a  conspicuous  and  familiar  form. 

69.  The    sporophyte.  —  The   pine    "  tree "    is   of    course 
a  sporophyte  that  has  become  very  large  (Fig.  93).     The 
vascular  cylinder  of  the  stem  is  thick,  and  it  becomes  thicker 
each  year  by  adding  new  layers  of  wood.     This  continual 
increase  in  the  amount  of  water-conducting  tissue  makes  wide 
and  continued  branching  possible,  for  branching  means   an 
increase  in  leaf  display,  and  increased  leaf  display  means 
a  larger  supply  of  water  not  only  for  food  manufacture,  but 
chiefly  to  supply  the  loss  from  the  leaves.     The  tree  type 
of  body,  with  its  tall  trunk  and  spreading  branches  bearing 
a  great  mass  of   foliage,   is   the   most   advanced   type   of 
sporophyte   body.      In   other  words,   it  is   the   sporophyte 
at  its  best. 

In  the  pine  the  leaves  are  not  broad,  being  only  green 
•"  needles,"  but  they  are  very  numerous  (Fig.  95).  There 
are  Conifers,  however,  with  broad  leaves,  and  the  Cycads 
have  very  large  fern-like  leaves  (Fig.  94). 

70.  The  strobili.  —  A  pine  tree  bears  two  kinds  of  strobili 
("  cones  "),  but  many  Gymnosperms  have  the  two  kinds  of 
strobili  on  different  trees.     The  pine  cone  that  is  ordinarily 
seen  is  the  strobilus  that  bears  megasporangia ;  that  is,  it  is 
a  group  of  megasporophylls.     It  is  so  much  larger  and  more 
persistent  than  the  other  kind  that  to  most  people  it  seems 
to  be  the  only  kind  of  cone  on  the  tree.     But  there  are  also 
small  strobili  composed  of  groups  of  microsporophylls  bear- 
ing microsporangia  (Fig.  95). 

Ovulate  strobilus.  —  If  one  of  the  larger  cones  of  the  pine 
is  cut  through  lengthwise  (Fig.  96,  A),  it  will  be  found  to 


SPERMATOPHYTES 


119 


consist  of  a  central  axis  bearing  numerous  close-set  mega- 
sporophylls,  which  are  very  firm,  and  finally  become  very 
hard.  On  the  upper  side  of  each  megasporophyll  near  the 


, a 


FIG.  95.  —  Tip  of  a  pine  branch,  showing  ovulate  cones  of  first  year  (a),  second  year 
(6),  and  third  year  (c) ;   also  a  cluster  of  staminate  cones  (d). 

base  are  two  megasporangia,  lying  side  by  side  (Fig.  96,  B 
and  C).  The  megasporophylls  lie  so  close  together  that  the 
megasporangia  cannot  be  seen  from  the  outside,  but  when  the 


120 


ELEMENTARY    STUDIES    IN   BOTANY 


strobilus  matures,  the  hard  megasporophylls  spread  apart 
and  the  megasporangia  become  exposed. 

These  structures  of  Seed-plants  were  known  long  before 
the  corresponding  structures  of  the  lower  groups,  and  of 
course  they  received  names.  It  is  necessary  now  to  fit  the 

two  sets  of  names  to- 
gether, so  as  to  recog- 
nize what  the  old  names 
really  stand  for.  The 
megasporophylls  of 
Seed-plants  were  called 
carpels,  long  before  they 
were  known  to  represent 
structures  belonging  to 
Pteridophytes.  Ap- 
proaching them  from 
the  Pteridophytes,  we 
find  that  the  so-called 
carpel  of  Seed-plants  is 
a  megasporophyll,  and 
this  is  an  illustration  of 
what  was  meant  when 
it  was  stated  that  a 
lower  group  of  plants 
explains  a  higher  one. 

The  megasporangia  of 
Seed-plants  were  called 

ovules  (the  structures  that  become  seeds),  and  thus  we  learn  that 
the  ovules  of  Seed-plants  are  megasporangia.  This  is  im- 
portant, because  ovule  means  "  a  little  egg,"  and  the  thought 
was  that  the  ovule  is  an  egg.  The  previous  chapters  have 
made  it  plain  that  an  egg  and  a  sporangium  are  about  as 
different  as  two  structures  can  be;  not  only  that,  but  that 
the  egg  belongs  to  the  gametophyte,  and  the  sporangium  to 
the  sporophyte.  The  word  " ovule"  is  not  likely  to  be  dis- 


FIG.  96.  —  Ovulate  cone  of  pine  :  A ,  cone  partly 
sectioned,  showing  the  central  axis  and  the 
overlapping  carpels  ("scales")  bearing  ovules 
(megasporangia)  near  the  base ;  B  and  C, 
single  carpels,  showing  the  pair  of  ovules 
borne  on  the  upper  side. 


SPERMATOPHYTES 


121 


carded,  although  its  real  meaning  records  a  mistake,  for  it 
has  been  long  used  and  is  shorter  than  megasporangium. 
In  using  it,  however,  it  must  be  realized  that  "  ovule  "  is 
just  another  name  for  the  megasporangium  of  Seed-plants. 
It  is  convenient  to  have  a  name  to  distinguish  the  stro- 
bilus  that  bears  ovules 
(megasporangia)  from 
the  one  that  does  not, 
and  the  most  appropri- 
ate one  seems  to  be 
ovulate  strobilus  or  ovu- 
late  cone.  Some  persist 
in  calling  the  ovulate 
cone  the  "  female  cone  "  ; 
but  the  cone  (strobilus) 
is  made  up  of  sporo- 
phylls  borne  by  a  spo- 
rophyte,  so  that  it  can- 
not very  well  be  either 
male  or  female,  terms 

FIG.  97.  —  Staminate  cone  of  pine :    A,  longi- 

that    belong     tO    the     ga-  tudinal  section  of  cone,  showing  the  stamens 

mo+rmUxH-o  (microsporophylls)  bearing    pollen  sacs  (mi- 

tupliy  l/e.  crosporangia)  upon  the  under  side  ;  B,  views 

Staminate  strobilus.  —          of  stamen  from  the  side  and  from  below> 

the  latter  showing    the  two  pollen  sacs;    C, 

The  Smaller  COne  Of  the  cross-section  of  a  stamen,  showing  the  two 

•  n      i          £  i  pollen  sacs  containing  pollen  grains   (micro- 

pine     Will     DC     IOUnd     tO  spores)  ;    D,  a  winged  pollen  grain,  showing 

consist  of  microsporo-  ™^n  the  early  cells  of  the  male  gameto" 
phylls  borne  upon  a  cen- 
tral axis,  much  smaller  and  more  delicate  than  the  megasporo- 
phylls  (Fig.  97,  A).  On  the  under  side  of  each  microsporo- 
phyll  are  two  microsporangia,  lying  side  by  side  (Fig.  97, 
B  and  C).  The  old  names  for  these  structures  among  Seed- 
plants  are  as  follows :  the  microsporophylls  were  called 
stamens,  the  microsporangia  were  called  pollen  sacs,  and  the 
microspores  were  called  pollen  grains  or  simply  pollen.  In 
this  way  it  has  become  evident  that  such  well-known  struct- 


122 


ELEMENTARY    STUDIES   IN   BOTANY 


ures  among  Seed-plants  as  stamens,  pollen  sacs,  and  pollen 
grains,  correspond  to  the  microsporophylls,  microsporangia, 
and  microspores  of  the  Pteridophytes. 

Since  stamen  is  so  much  more  convenient  a  term  than 

microsporophyll,  the  cone 
which  bears  microspo- 
rangia (pollen  sacs)  may 
be  called  the  staminate 
strobilus  or  staminate  cone, 
but  it  should  be  realized 
that  "  stamen  "  is  only 
another  name  for  the 
microsporophyll  of  Seed- 
plants.  It  is  the  stami- 
nate cone  that  is  often 
called  a  "  male  cone," 
which  is  no  more  appro- 
priate than  to  call  the 
ovulate  cone  a  "  female 
cone."  Also,  there  is  no 
objection  to  calling  the 
microspores  "  pollen," 
provided  it  is  remembered 
that  "  pollen  "  is  only 
another  name  for  the  mi- 
crospores of  Seed-plants. 
71.  The  ovule. —  It  is 
the  ovule  (megasporan- 
gium)  that  distinguishes 
Seed-plants,  for  it  devel- 
ops into  the  seed,  and 

therefore  it  must  differ  somewhat  from  the  megasporangia 
of  Pteridophytes.  If  it  is  cut  through  lengthwise,  its  general 
structure  will  be  evident  (Fig.  98,  A).  On  the  outside  of  it 
there  is  a  covering  which  is  loose  above  and  extends  into  a 


A  B 

PIG.  98.  —  A,  section  of  scale  of  ovulate  cone, 
showing  the  bract  beneath  (6),  the  scale 
(s),  the  ovule  (o),  with  its  integument  and 
nucellus,  and  within  the  nucellus  the  mega- 
spore  (0)  which  probably  contains  the  be- 
ginning of  the  female  gametophyte ;  B,  a 
section  through  the  ovule  a  year  later, 
showing  the  large  female  gametophyte  (g) 
with  two  archegonia  (a)  which  are  being 
reached  by  pollen  tubes  (t)  penetrating  the 
tip  of  the  nucellus;  observe  also  the  in- 
tegument at  the  top  of  the  ovule  with  its 
passage  way  (micropyle)  to  the  nucellus. 


SPERMATOPHYTES  123 

more  or  less  extended  tube.  The  covering  is  the  integument, 
and  the  tube  is  the  micropyle  ("  little  gate  ").  Within  the 
covering  is  the  body  of  the  ovule  (nucellus),  with  its  tip  at 
the  base  of  the  open  micropyle.  If  the  ovule  is  a  mega- 
sporangium,  it  must  contain  megaspores,  and  these  are  found 
in  the  nucellus.  Several  megaspores  start,  but  only  one 
grows,  and  it  becomes  so  large  that  it  looks  like  a  cavity  in 
the  middle  of  the  nucellus  (Fig.  98,  A).  The  peculiarity  of 
this  megasporangium  (the  ovule)  is  not  that  it  has  only  one 
megaspore,  or  that  the  megaspore  is  so  large,  but  that  it  is 
never  shed,  that  is,  it  never  escapes  from  its  megasporangium. 
The  fact  that  this  megaspore  is  retained  in  its  sporangium  is- 
the  reason  why  the  ovule  becomes  a  seed. 

72.  The  stamen.  —  There  is  nothing  peculiar  about  the 
stamen  (microsporophyll),  except  that  among  Gymnosperms 
it  becomes  more  and  more  unlike  a  leaf  in  appearance.     In 
some  Cycads  it  appears  as  a  flat  blade  bearing  sporangia 
(pollen  sacs)  on  its  under  surface  ;  in  pines  the  blade  becomes 
short-stalked  (Fig.  97,  B) ;  and  in  many  other  Gymnosperms 
the  stalk  becomes  elongated  and  the  blade  reduced  to  a  plate 
or  knob  bearing  the  pollen  sacs.     When  two  regions  of  a 
stamen  are  distinguishable  as  a  stalk  region  and  a  pollen-sac 
region,  the  former  is  called  the  filament,  and  the  latter  the 
anther.     These   names   are   often   convenient  in   describing 
stamens,  but  they  only  mean  that  some  microsporophylls 
have  stalks  distinct  from  the  sporangium-bearing  region. 

73.  The  gametophytes.  —  In  the  preceding  chapter  (§  63, 
p.  110)  it  was  stated  that  the  gametophytes  of  heterosporous 
Pteridophytes  do  not  emerge  from  the  spores  that  produce 
them.     Of   course   all   Seed-plants  are  heterosporous,  and, 
therefore,  just  as  in  heterosporous  Pteridophytes,  the  male 
gametophyte  develops  within  the  microspore  (pollen  grain), 
and  the  female  gametophyte  develops  within  the  megaspore 
which    is    retained    within    the    megasporangium    (ovule). 
This  means  that  in  Seed-plants  the  gametophytes  are  in- 


124  ELEMENTARY   STUDIES   IN   BOTANY 

visible  to  the  ordinary  observer,  for  they  are  living,  like  in- 
ternal parasites,  within  structures  of  the  sporophyte. 

The  female  gametophyte.  —  The  large,,  solitary  megaspore 
within  the  ovule  develops  within  itself  the  female  gameto- 
phyte, which  consists  of  numerous  cells  (Fig.  98,  B).  Cells 
on  the  side  of  the  gametophyte  towards  the  tip  of  the  nucel- 
lus,  which  means  also  towards  the  micropyle,  develop 
archegonia  (Fig.  98,  B),  and  in  each  archegonium,  of  course, 
there  is  an  egg.  It  becomes  evident  now  that  an  "  ovule  "  is 
very  far  from  being  an  egg,  although  it  received  its  name  be- 
cause it  was  thought  to  be  an  egg.  It  is  helpful  in  fixing  the 
relations  of  parts  to  remember  that  the  egg  is  in  an  archego- 
nium, the  archegonium  is  produced  by  the  gametophyte,  the 
gametophyte  is  within  the  megaspore,  and  the  megaspore 
is  within  the  ovule  (megasporangium) .  Of  course  the  egg 
is  passive  and  remains  in  the  archegonium,  awaiting  fertiliza- 
tion. 

The  male  gametophyte.  —  The  microspores  (pollen  grains) 
do  not  remain  within  the  microsporangia  (pollen  sacs), 
but  are  discharged  and  are  widely  scattered  by  the  wind. 
When  the  pollen  of  pines  is  being  shed,  the  air  is  sometimes 
full  of  the  small  "  grains  "  (spores),  which  look  like  yellow 
powder,  and  they  settle  down  like  rain.  In  the  pines,  the 
pollen  grains  have  wings  (Fig.  97,  Z>),  but  this  is  not  true  of 
all  Conifers.  Of  course  very  few  pollen  grains  land  on  the 
right  spots,  but  there  are  so  many  of  them  that  some  reach 
the  proper  landing  places.  The  "  right  spots  "  are  the  ovulate 
cones,  whose  hard  megasporophylls  (carpels),  often  called 
the  "  scales  "  of  the  cone,  have  spread  apart  to  receive  them. 
The  minute  pollen  grains  slip  down  the  sloping  scale  and  col- 
lect in  a  little  drift  at  the  bottom,  around  the  projecting 
micropyle.  Then  some  of  them  get  into  the  micropyle  and 
reach  the  tip  of  the  nucellus,  which  is  their  destination.  This 
transfer  of  pollen  from  the  pollen  sacs  (microsporangia) 
to  the  ovulate  cone,  and  in  the  cone  to  the  tip  of  the  nucellus, 


SPERMATOPHYTES 


125 


FIG.  99.  —  Two  views  of  the  sperm  of  a  Cycad, 
showing  its  spiral  form  and  many  cilia. 


is  called  pollination,  and  in  the  Gymnosperms  the  agent  of 
this  transfer  is  the  wind.  Such  plants,  therefore,  are  said 
to  be  wind-pollinated. 

Before  the  pollen  grains  (microspores)  leave  the  pollen 
sacs,  the  male  gametophyte  has  begun  to  develop  within 
them  (Fig.  97,  D),  and 
after  the  pollen  has 
reached  the  nucellus, 
the  gametophyte  con- 
tinues to  develop,  form- 
ing an  antheridium, 
which  in  almost  every 
Gymnosperm  produces 
two  sperms.  In  the 
Cycads  these  sperms 
have  cilia  and  swim  (Fig.  99),  just  as  do  those  of  the 
Pteridophytes ;  but  in  the  Conifers  the  sperms  have  no 
cilia,  and  of  course  do  not  swim. 

74.  Fertilization.  —  After  pollination  has  been  accom- 
plished, and  the  pollen  grain  (microspore)  of  the  pine,  with 
its  contained  male  gametophyte,  is  resting  on  the  tip  of  the 
nucellus,  the  sperms  and  the  eggs  are  separated  from  one 
another  by  the  mass  of  tissue  that  forms  the  top  of  the  nucel- 
lus. This  tissue  must  be  penetrated,  and  the  pollen  grain 
(really  the  male  gametophyte  within  it)  puts  out  a  tube 
(pollen  tube)  which  grows  into  it,  crowding  its  way  among  the 
cells,  absorbing  nourishment  from  them  like  an  internal 
parasite,  and  finally  reaches  the  egg  (Fig.  98,  B).  In  the  tip 
of  the  advancing  tube  the  two  sperms  are  tying,  and  when  the 
vicinity  of  the  egg  is  reached,  they  are  discharged  from  the 
tube,  and  one  of  them  penetrates  the  egg  and  the  two  nuclei 
fuse.  The  result,  of  course,  is  a  fertilized  egg  lying  deep  in 
the  ovule. 

Pollination  and  fertilization  should  not  be  confused,  as 
they  often  are.  When  pollen  is  carried  to  an  ovulate  cone 


126 


ELEMENTARY    STUDIES   IN   BOTANY 


of  a  pine  (or  to  a  flower  in  higher  plants)  it  is  often  called 
"  fertilization/'  but  it  is  evident  that  it  is  not.  Pollination 
is  a  performance  that  must  precede  fertilization,  and  it  may 
or  may  not  be  followed  by  fertilization,  which  is  the  fusion 
of  a  sperm  and  an  egg. 

75.  The  embryo.  —  The  fertilized  egg,  lying  within  the 
ovule,  begins  to  germinate  almost  at  once,  and  as  the  young 

sporophyte  (embryo) 
grows,  it  feeds  upon  the 
surrounding  cells  of  the 
female  gametophyte,  and 
finally  reaches  a  stage 
in  which  the  different 
parts  become  distinguish- 
able (Fig.  100,  A).  In 
the  pine,  the  three  re- 
gions are  a  stem-like  part 
(hypocotyl)  whose  tip  is 
directed  towards  the  top 
of  the  nucellus  (which 
means  that  it  is  directed 

towards    the    micropyle)  J 

a  rosette  of  leaf-like 
parts  (cotyledons) ;  and  in 
the  midst  of  the  rosette 

of  cotyledons,  and  resting  on  the  top  of  the  hypocotyl, 
a  minute  bud-like  part  (plumule).  The  hypocotyl  will  later 
develop  the  root,  the  plumule  will  develop  the  stem  and 
leaves,  and  the  cotyledons  will  for  a  short  time  supply 
nourishment  to  the  young  plant. 

Although  the  fertilized  egg  germinates  almost  at  once,  and 
the  embryo  grows  until  the  three  regions  described  appear, 
it  does  not  continue  to  grow  without  interruption,  but  passes 
into  what  is  called  the  dormant  ("  sleeping  ")  stage,  and  the 
dormant  embryo  is  one  of  the  peculiarities  of  Seed-plants. 


FIG.  100.  —  A,  section  of  a  pine  seed,  showing 
the  hard  coat  (testa),  the  female  gameto- 
phyte  (dotted)  which  has  grown  to  the  testa 
and  is  usually  called  endosperm,  and  the 
embryo  (also  sectioned)  with  its  hypocotyl, 
its  cotyledons  (three  only  are  shown),  and 
the  plumule  (the  short  protuberance)  sur- 
rounded by  the  cotyledons ;  B  and  C,  ger- 
mination of  the  pine  seed,  the  cotyledons 
backing  out  of  the  testa  in  B  and  entirely 
free  in  C. 


SPERMATOPHYTES  127 

Just  what  conditions  result  in  dormancy  we  do  not  know  in 
all  cases,  but  we  do  know  some  facts  that  are  associated 
with  it.  What  these  are  will  be  described  in  the  next  section. 

76.  The  seed.  —  While  the  embryo  is  being  formed, 
changes  are  taking  place  in  the  integument  of  the  ovule. 
A  new  kind  of  tissue  begins  to  develop  from  the  cells  of  the 
integument,  and  continues  to  develop  until  it  forms  a  hard 
covering  that  completely  invests  the  ovule,  the  only  breaks 
in  it  being  at  the  micropyle  (whose  position  is  indicated  by 
what  looks  like  a  small  scar)  and  at  the  point  where  the  ovule 
(megasporangium)  was  attached  to  the  carpel  (mega- 
sporophyll).  When  this  hard  coat  (testa)  is  complete,  the 
ovule  has  become  a  seed  (Fig.  100,  A). 

It  is  evident  that  the  seed  is  a  very  complex  structure,  and 
that  it  has  resulted  from  the  retention  of  the  megaspore 
within  the  megasporangium  (ovule),  so  that  within  this 
sporangium  the  female  gametophyte  develops,  fertilization 
takes  place,  and  the  young  sporophyte  (embryo)  is  formed. 
In  a  seed,  therefore,  three  generations  are  represented : 

(1)  the  old  sporophyte,  represented  by  the  ovule  structures ; 

(2)  the  female  gametophyte,  very  commonly  called  the  en- 
dosperm of  seeds ;   and  (3)  the  young  sporophyte  (embryo) . 
It  is  a  simple  thing  to  observe  the  structure  of  a  seed  and  to 
watch  its  "  germination,"  but  really  to  know  the  structure 
of  a  seed  needs  the  approach  to  it  from  the  lower  groups  of 
plants. 

A  seed  is  said  to  "  germinate,"  but  it  is  plain  that  it  is  not 
germination  in  the  sense  we  have  been  using  that  word,  for 
only  spores  and  fertilized  eggs  (oospores)  germinate.  Besides, 
germination  occurs  when  the  fertilized  egg  within  the  ovule 
produces  the  embryo;  therefore,  when  a  seed  is  said  to 
"  germinate,"  the  real  germination  had  occurred  long  before, 
usually  the  preceding  season,  sometimes  many  seasons 
before.  What  "  seed  germination  "  means,  therefore,  is  not 
real  germination,  but  the  "  awakening "  of  the  young 


128  ELEMENTARY    STUDIES   IN   BOTANY 

sporophyte  (embryo)  from  its  dormant  condition,  and  the 
resumption  of  its  growth,  and  its  escape  from  the  seed  coat 
(Fig.  100,  B  and  C).  Of  course  seeds  will  always  be  said  to 
"  germinate,"  for  the  word  is  too  firmly  established  in  this 
connection  to  be  changed,  but  the  student  of  botany  should 
realize  that  "  seed-germination  "  is  not  the  starting  of  a  new 
individual  (which  is  real  germination),  but  the  continued 
growth  of  an  individual  that  has  been  started  already.  The 
resumed  growth  of  the  embryo,  and  its  escape  as  a  "  seed- 
ling," will  be  considered  in  connection  with  the  other  great 
group  of  Seed-plants,  whose  seeds  are  those  most  frequently 
"  germinated  "  by  those  who  cultivate  plants. 

77.  Summary.  —  The  Gymnosperms  are  the  most  ancient 
Seed-plants,  continuing  and  advancing  the  structures  of  the 
Ferns,  from  which  they  differ  chiefly  in  the  presence  of  seeds. 
The  vascular  system  is  notably  developed,  resulting  in  larger 
sporophyte  bodies,  and  in  a  greater  display  of  foliage.  The 
earliest  Gymnosperms  did  not  have  strobili,  resembling  the 
Ferns  in  this  feature,  but  all  other  Gymnosperms  have 
strobili  as  a  very  conspicuous  feature. 

The  important  fact  about  Gymnosperms,  however,  is 
the  existence  of  seeds.  A  seed  is  derived  from  an  ovule, 
and  an  ovule  is  a  megasporangium.  The  difference  between 
an  ovule  and  any  other  megasporangium  is  that  the  ovule 
retains  its  megaspores  instead  of  shedding  them.  This  re- 
tention of  the  megaspore  means  that  the  female  gameto- 
phyte  develops  within  the  ovule,  that  fertilization  occurs 
there,  and  that  the  embryo  sporophyte  develops  there. 
When  all  of  these  structures  within  the  ovule  become  in- 
cased by  a  hard  coat  (testa),  the  total  structure  is  the  seed. 

The  transportation  of  pollen  (pollination)  is  effected  by 
the  wind,  and  after  fertilization  the  embryo  develops  three 
regions  (hypocotyl,  cotyledons,  and  plumule)  and  then 
passes  into  a  dormant  stage.  Activity  is  resumed  when  the 
conditions  for  "  seed-germination  "  are  present. 


CHAPTER  VIII 
SPERMATOPHYTES.  —  2.  ANGIOSPERMS 

THE  REAL  FLOWERING  PLANTS 

78.  General  character.  —  The  Angiosperms  have  several 
superlative  features.  They  are  the  most  advanced,  the  most 
recent,  the  most  conspicuous,  and  the  most  useful  of  plants. 
The  vegetation  that  covers  the  earth  is  in  the  main  angio- 
sperm  vegetation,  and  when  to  this  is  added  the  fact  that  the 
Angiosperms  are  almost  the  only  plants  that  men  use,  it 
is  not  strange  that  they  were  once  thought  to  be  the  only 
plants  worth  studying.  Perhaps  the  best  reason  for  study- 
ing the  lower  groups  is  that  Angiosperms  may  be  understood 
better.  Some  more  definite  appreciation  of  the  relative 
abundance  of  Angiosperms  may  be  obtained  from  the  state- 
ment that  about  450  different  kinds  (species)  of  living 
Gymnosperms  are  known,  while  about  130,000  different 
kinds  of  Angiosperms  have  been  recorded. 

In  the  preceding  chapter  (§  66)  it  was  stated  that  An- 
giosperms differ  from  Gymnosperms  in  having  the  seeds 
inclosed.  The  inclosing  structure  is  the  carpel,  which  thus 
forms  a  "  seed-vessel  "  of  extremely  variable  appearance. 
Using  the  terms  applied  to  these  structures  in  the  lower 
groups,  the  statement  would  be  that  the  megasporophyll 
incloses  the  megasporangia  (ovules) .  It  must  not  be  thought 
that  the  inclosure  of  the  ovules  is  the  only  character  that 
distinguishes  Angiosperms  from  Gymnosperms.  It  is  so 
obvious  a  feature  that  it  suggested  the  name  of  the  group, 
but  there  are  many  other  important  differences. 

129 


130  ELEMENTARY   STUDIES   IN   BOTANY 

79.  The  sporophyte.  --The  habit  of  the  sporophyte,  as 
its  general  appearance  is  called,  shows  every  possible  variation, 
as  would    be   expected  in   so    large  a  group.     One  of  the 
oldest  groupings  of  plants  recognized  this  fact  in  classifying 
them  as  herbs,  shrubs,  and  trees.     Of  course  these  names 
are  retained   for  general  use,  but  they  cannot  be  denned 
with  exactness. 

The  sporophyte  is  extremely  variable  not  only  in  habit, 
but  also  in  structure.  In  general,  the  structure  of  the  stems 
and  leaves  is  quite  different  from  that  found  among  Gymno- 
sperms,  almost  every  trace  of  the  ancient  fern  connection 
having  disappeared.  The  root,  stem,  and  leaf  are  such 
important  organs  that  they  deserve  separate  treatment,  and 
this  has  been  deferred  until  the  greatest  display  of  these 
organs  has  been  reached  in  the  Angiosperms.  Their  place 
in  the  history  of  the  plant  kingdom  has  been  stated,  but  it 
remains  to  consider  their  work,  especially  as  such  knowledge 
is  essential  to  any  intelligent  cultivation  of  plants.  This 
subject  will  be  treated  in  subsequent  chapters. 

80.  The  flower.  —  The  most  characteristic  structure  of 
Angiosperms  is  the  flower.     This  does  not  mean  that  all 
Angiosperms  have  flowers,  but  that  Angiosperms  have  de- 
veloped the  flower.     In  §  61  (p.  107)  it  was  stated  that  the 
strobilus  is  the  precursor  of  the  flower.     Throughout  Gym- 
nosperms  the  strobilus  is  the  nearest  approach  to  the  flower, 
and  among  the  simpler  Angiosperms  the  strobilus  continues. 

It  is  necessary  to  have  clearly  in  mind  the  distinction 
between  a  strobilus  and  a  flower.  It  is  a  distinction  of  con- 
venience and  riot  of  exactness,  for  the  two  structures  grade 
insensibly  into  one  another.  A  strobilus  is  a  group  of  sporo- 
phylls,  organized  together  so  as  to  form  a  structure  distinct 
from  the  foliage-bearing  part  of  the  plant.  A  strobilus- 
bearing  plant,  therefore,  has  two  kinds  of  lateral  members : 
sporophylls.  and  leaves.  A  flower  introduces  a  thirdJateral 
member,  the  perianth,  which  is  associated  with  the  sporo- 


SPERMATOPHYTES 


131 


phylls.     A  flower,  therefore,  may  be  said  to  be  a  strobilus 
with  a  perianth.     Originally  a  flower  was  thought  to  be 
essentially  a  group  of  sex-organs,   and  therefore  a  sexual 
structure.     It  is  evident  that  it  consists  of  members  (peri- 
anth and  sporophylls)  borne  by  a  sporophyte,  and  there- 
fore it  cannot  be  a  sexual  structure.     It  is  impossible  to 
apply  the  term  strobilus  and  flower  strictly  among  Angio- 
sperms,  for  some  flowers  have  no  perianth  because  they  have 
never    had    one,    and 
therefore   are   strobili; 
and    others    have    no 
perianth  because  they 
have  lost  it,  and  there- 
fore are  flowers  by  de- 
scent.    Among  Angio- 
sperms,  therefore,  it  is 
convenient  to  speak  of 
all    sporophyll-bearing        -^  j  / 

structures  as  flowers. 

81.     The  perianth.  /FlG    101  _  Flower   of   peony:    &,  sepals    (forming    J 

It   is    evident    that    the     \      the    calyx);     c>    Petals    (forming    the   corolla); 

calyx  and  corolla^  together  constiiuig  the  perir 

perianth    IS    the   distin-     j     "SS&Z  a,  starnenTf  O,  carpels  (oT^istils).  —  After 
.   ,  .  i  r  ,      STRASBURGER. 

guishing    mark    of    a    \ 

flower;  in  fact,  it  is  just  the  mark  that  people  in  general 
use  in  recognizing  a  flower.  One  of  the  features  of  Angio- 
sperms  is  the  endless  variation  in  the  structure  of  the 
perianth,  so  that  the  different  kinds  of  flowers  become  the 
most  valuable  means  of  classifying  Angiosperms. 

The  term  perianth  is  a  collective  one,  to  include  all  the 
members ;  but  it  is  used  chiefly  in  cases  where  the  members 
are  all  approximately  alike,  as  in  the  lilies  and  their  allies. 

\  In  most  Angiosperms,  however,  the  perianth  is  differentiated 
into  two  sets,  calyx  and  corolla  (Fig.  101).  The  calyx, 
whose  individual  members  are  called  sepals,  is  the  outer 

\set   and  usually  green  in  color;   while  the    corolla,  whose 


132 


ELEMENTARY   STUDIES   IN   BOTANY 


individual  members  are  called  petals,  is  variously  and  usually 
brightly  colored,  forming  the  showy  part  of  the  flower. 
In  fact,  it  is  the  corolla  that  usually  gives  character  and  at- 
traction to  the  flower.  These  general  statements  in  reference 
to  the  calyx  and  corolla  must  not  be  applied  too  rigidly. 
For  example,  the  calyx  may  be  brightly  colored  and  showy, 


FIG.  102.  —  Flower  of  tobacco  :  A,  sympetalous  corolla  ;  B,  tube  of  corolla  cut  open  and 
showing  stamens ;  C,  the  pistil  (carpels),  showing  ovary  and  style  (the  stigma  forms 
the  surface  of  the  knob-like  tip  of  the  style).  —  After  STRASBURGER. 


the  corolla  may  not  be  showy  or  even  colored,  both  sets  may 
be  showy,  neither  set  may  be  showy  or  colored,  etc. 

The  general  roles  played  by  calyx  and  corolla  have  to  do 
with  the  sporophylls.  The  calyx  protects  the  young  and 
growing  parts  within  while  the  flower  is  in  bud.  The  showy 
corolla  is  related  in  some  way  to  the  visits  of  certain  insects 
(as  bees,  butterflies,  moths,  etc.),  which  become  agents  in 
transporting  pollen  (pollination ,  see  §  73,  p.  125).  This  sub- 


SPERMATOPHYTES 


133 


iect  of  the  relation  of  insects  to  flowers  is  a  very  large  one, 
and  will  be  presented  in  the  following  chapter. 

The  great  variation  in  the  structure  of  the  corolla  is  the 
variation  of  chief  service  in  classification,  so  far  as  the  peri- 
anth is  concerned.  A  great  many  terms  have  been  applied 
to  the  different  conditions  of  the  corolla,  and  a  few  of  the 
most  significant  conditions  are  as  follows.  The  simplest 
kind  of  corolla  is  one  in  which  the  petals  are  free  from  one 
another  and  are  all  alike.  Such  a  corolla  is  said  to  be  poly- 
petalous  (of  "  many  petals  ")  and  regular.  In  many  flowers 


B 


E 


FIG.  103.  —  Sympetalous  flowers:  A,  bluebell;  B,  phlox;  C,  deadnettle;  D,  snap- 
dragon ;  E,  toadflax ;  C,'  D,  E  are  irregular  flowers  (bilabiate  in  this  case) .  —  After 
GRAY. 

the  petals  appear  as  if  united  to  form  tubes,  bells,  funnels, 
etc.  (Figs.  102  and  103),  and  such  a  corolla  is  said  to  be 
sympetalous  ("  petals  together  ").  This  sympetalous  con- 
dition is  so  constant  in  families  of  plants,  that  the  highest 
one  of  the  three  great  groups  of  Angiosperms  is  named  the 
Sympetalce,  because  in  all  of  its  families  the  flowers  are 
sympetalous.  In  certain  families  the  petals  of  a  flower  are 
not  all  alike ;  and  then  the  corolla  is  said  to  be  irregular. 
For  example,  the  sweet  pea  and  its  allies  have  very  irregular 
flowers,  the  petals  being  very  much  unlike,  but  the  corolla 
is  polypetalous.  In  the  snapdragon,  which  is  sympetalous, 
the  rim  of  the  tube  has  the  appearance  of  two  unequal  lips, 
10 


134 


ELEMENTARY   STUDIES   IN   BOTANY 


three  of  the  petals  entering  into  the  structure  of  the  upper 
lip,  and  the  other  two  petals  forming  the  lower  lip  (Fig.  103, 
C,  D,  E).  Such  a  corolla  is  naturally  called  bilabiate  ("  two- 
lipped  "),  and  a  large  family  of  the  Sympetalae  is  called  the 
Labiatce  ("  lipped  ")  because  its  flowers  have  this  two-lipped 
structure.  These  are  simply  conspicuous 
illustrations  of  irregular  corollas. 

82.  The  stamen.  —  It  was  among  the 
Angiosperms  that  the  name  stamen  was 
given  long  ago  to  the  sporophyll  that 
bears  microsporangia,  and  since  it  was 
recognized  to  be  necessary  to  seed-forma- 
tion, it  was  thought  to  be  the  male  organ, 
and  the  pollen  grains  (microspores)  it 
produced  were  thought  to  be  male  cells. 

FlGof\^e^mr°st«Sr    Jt  is  eyident   tnat   sporophylls   and  mi- 
showing  filament  and    crospores   belong   to   the   sporophyte,   a 

anther,  the  latter  ap-  ,  .      ,.     .  ,        , 

sexless   individual,  so  that    the    stamen 
cannot  be  a  male  organ.     The  mistake 


which  the  sac  splits 
to  discharge  the  pol- 
len. —  After  SCHIM- 
PEB. 


chiefly  as  two 
pollen  sacs  ;  the  ver- 
tical line  shown  in 

the  left  pollen  sac  of    was  natural,  because  the  minute  gameto- 

the    left    stamen    in- 

dicates  the  line  along    phytes  had  not  been  discovered. 

The  stamens  of  Angiosperms  vary  ex- 
tremely in  appearance,  but  in  most  cases 
two  distinct  regions  can  be  recognized 
(Fig.  104).  There  is  a  stalk-like  region,  which  is  long  or 
short,  slender  or  broad,  called  the  filament,  and  a  terminal 
region  that  bears  the  microsporangia,  called  the  anther. 
The  filament  puts  the  anther  in  a  favorable  position  for  dis- 
charging its  pollen  grains,  which  are  to  be  carried  away  by 
the  wind  or  by  insects  or  by  some  other  agency. 

The  anther  consists  of  the  top  of  the  sporophyll  and  usually 
four  microsporangia,  two  on  each  side  (Fig.  105).  As  the 
microsporangia  grow,  the  two  on  each  side  usually  run  to- 
gether and  become  one  cavity  (Fig.  106),  so  that  in  the  mature 
anther  there  are  usually  two  sacs  (Fig.  104)  containing  pollen 


SPERMATOPHYTES 


135 


grains  (microspores).     It  is  these  sacs,  usually  consisting  of 
two   fused   microsporangia,   that  are   called    pollen-sacs   in 


FIG.  105.  —  Cross-section  of  a  very  young  anther  of  a  lily,  showing  the  four  developing 

sporangia. 

Angiosperms.     A  pollen-sac  opens  to  discharge  the  pollen, 
usually  by  splitting  down  the  line  where  the  two  microspo- 


FIG.  106.  —  Cross-section  of  a  mature  anther  of  a  lily  (much  larger  than  that  shown  in 
Fig.  105),  showing  the  two  chambers  formed  by  the  four  sporangia,  and  also  the 
region  of  opening  for  each  chamber  (s). 


136 


ELEMENTARY   STUDIES   IN   BOTANY 


rangia  come  together  (Fig.  104),  but  sometimes  there  is 
formed  an  opening  (pore)  at  the  top,  which  may  even  be 
extended  into  a  tube  (Fig.  107). 

The  stamens,  like  the  petals  and  sepals,  are  not  always 
free  from  one  another,  for  sometimes  the  filaments  appear 
as  if  they  had  been  united.  In  some  plants,  for  example, 


FIG.  107.  —  Anthers  opening  by  terminal  pores:  A,  potato  or  tomato;    B,  arbutus; 
C,  cranberry  or  huckleberry.  —  A  and  B  after  ENGLER  and  PRANTL,  C  after  KEENER. 

the  stamens  appear  united  in  this  way  in  two  or  more  sets, 
and  sometimes  they. form  a  single  set,  all  of  the  filaments 
together  forming  a  tube  (Fig.  108).  In  sympetalous  corol- 
las it  is  usual  for  the  stamens  to  appear  as  if  arising  from  the 
tube  of  the  corolla  (Fig.  102,  £).  This  means  that  the  petal 
set  and  stamen  set  have  developed  together,  so  that  they  are 
not  distinct  from  one  another  at  base. 

While  the  two  kinds  of  sporophylls  (stamens  and  carpels) 
are  usually  associated  in  the  same  flower,  there  are  many 


SPERMATOPHYTES 


137 


Angiosperms  whose  flowers  contain  only  one  kind  of  sporo- 
phyll.  This  means  that  such  plants  have  two  kinds  of  flowers, 
one  containing  stamens,  and  the  other  containing  carpels. 
These  two  kinds  of  flowers  may  be  produced  by  the  same 
plant  or  by  different  plants.  In  the  latter  case,  there  are 
two  kinds  of  sporophytes,  differing  in  their  flowers,  one  kind 
bearing  staminate  flowers 
(with  stamens  only),  and 
the  other  kind  bearing  car- 
pellate  flowers  (with  car- 
pels only).  For  example, 


FIG.  108.  —  Section  of  a  flower  of 
Althaea,  showing  sepals  (a),  petals 
(6),  tube  of  stamens  (c)  inclosing 
the  style  (d),  and  also  the  ovules 
(e)  within  the  ovary.  —  After  BERG 
and  SCHMIDT. 


FIG.  109.  —  Indian  corn  (maize)  :  A, 
showing  the  "tassel"  (made  up  of 
staminate  flowers) ;  B,  showing  the 
ear  (made  up  of  carpellate  flowers) 
within  its  husk  and  the  exposed  "silk" 
(made  up  of  the  long,  protruding 
styles).  —  After  DEVRIES. 


the  corn  plant  has  the  two  kinds  of  flowers,  but  both  are 
borne  by  the  same  individual  (sporophyte),  the  staminate 
flowers  forming  the  "  tassel  "  and  the  carpellate  flowers 
the  "  ear "  (Fig.  109) ;  while  in  the  chestnut,  one  tree 
bears  staminate  flowers  (and  therefore  does  not  produce 
chestnuts)  and  another  tree  bears  the  carpellate  flowers. 

83.   The  carpel. — It  has  been  stated  that  the  term  "  carpel" 
has  been  applied  among  Seed-plants  to  the  structure  called 


138 


ELEMENTARY    STUDIES   IN   BOTANY 


megasporophyll  among  Pteridophytes ;  tnat  is,  the  carpel 
is  a  megasporophyll.  It  has  been  stated  also  that  the  angio- 
sperm  carpel  differs  from  that  of  the  Gymnosperms  in  in- 
closing the  megasporangia  (ovules),  the  number  inclosed 
ranging  from  one  to  very  many. 

In  forming  a  case  about  the  ovules,  two  regions  of  the  car- 
pel usually  become  evident  (Figs.  102,  C,  and  110)  :  (1)  a  more 
or  less  bulbous  region  that  incloses  the  ovules  (the  ovary), 

and  (2)  a  more  or  less 
extended  beak-like  re- 
gion arising  from  the 
ovary  (the  style) .  The 
name  ovary  was  given 
^vvhen  the  ovules  were 
thought  to  be  eggs, 
and  both  names  are 
unfortunate,  for  they 
imply  what  is  not  true, 
but  they  have  been 
used  for  so  long  a  time 
that  it  would  be  more 
confusing  to  replace 
them  than  to  retain 
them.  The  significance 

of  the  style  is  found  in  the  fact  that  it  provides  a  special  re- 
ceptive surface  (the  stigma)  for  the  pollen  grains,  and  the 
length  and  form  of  the  style  are  answers  to  the  problem  of 
the  most  favorable  position  for  the  stigma.  Very  commonly 
the  style  swells  into  a  knob  at  the  top,  and  the  surface  of  this 
knob  is  the  stigmatic  surface  (Figs.  102,  C,  and  110,  C). 
Sometimes  the  stigmatic  surface  extends  down  the  side  of 
a  style,  as  in  corn,  in  which  the  so-called  "  silk  "  is  made  up 
of  styles  (Figs.  109,  and  110,  B).  Rarely,  there  is  no  style 
at  all,  and  the  stigmatic  surface  is  upon  the  ovary  itself. 
It  is  evident,  therefore,  that  the  two  essential  features  of  an 


FIG.  110.  —  A,  simple  pistils  (each  one  a  single 
carpel)  ;  B  and  C,  compound  pistils  (each  one 
composed  of  several  carpels)  ;  in  B  the  stigma 
extends  along  the  sides  of  the  styles,  in  C  it  is 
on  the  terminal  knob  of  the  style.  —  After  BERG 
and  SCHMIDT. 


SPERMATOPHYTES 


139 


angiosperm  carpel  are  the  ovary  and  the  stigmatic  surface, 
and  that  a  style  is  generally  present  because  it  insures  a  more 
favorable  position  to  the  stigmatic  surface  for  receiving  the 
pollen. 

A  flower  may  have  a  single  carpel,  or  it  may  have  several. 
In  the  latter  case,  the  carpels  are  arranged  in  one  of  two 
ways :  (1)  they  may  be  distinct  from  one  another  (Fig.  110, 
A),  or  (2)  they  may  be  organized  together  in  a  single  body 
(Fig.  110,  B  and  C).  It  is  convenient  to  have  a  term  that 
may  be  applied  to  either  situation,  and  that  term  is  pistil. 


FIG.  111.  —  Cross-sections  of  ovaries  of  compound  pistils :  A,  three  carpels  forming  a 
"one-celled"  ovary;  B,  three  carpels  forming  a  "three-celled"  ovary.. —  After 
SCHIMPEB. 

A  pistil  is  a  single  structure,  with  its  ovary,  style,  and  stig- 
matic surface,  but  it  may  consist  of  a  single  carpel  or  of  two 
or  more  carpels  organized  together.  These  two  conditions 
of  the  pistil  are  distinguished  as  simple  pistils  and  compound 
pistils  (often  called  syncarpous  pistils,  which  means  pistils 
with  "  carpels  joined  together  ").  The  term  pistil,  there- 
fore, is  one  of  convenience  rather  than  of  exactness,  for 
sometimes  it  is  identical  with  carpel  and  sometimes  it  in- 
cludes two  or  more  carpels.  It  is  like  the  word  "  house, " 
which  may  include  one  room  or  two  or  more  rooms.  It  fol- 
lows that  there  are  three  possible  carpel  conditions  in  a  flower : 
(1)  a  solitary  carpel  and  therefore  a  single  pistil ;  (2)  two 
or  more  carpels  forming  as  many  pistils;  and  (3)  two  or 
more  carpels  forming  a  single  pistil. 


140 


ELEMENTARY   STUDIES   IN   BOTANY 


In  the  compound  (syncarpous)  pistil  there  are  two  dif- 
ferent conditions  of  the  ovary  that  must  be  mentioned.  In 
the  one  case,  the  carpels  are  arranged  so  as  to  inclose  a  single 
cavity,  as  if  open  carpels  had  united  edge  to  edge  (Fig.  Ill, 
A).  In  the  other  case,  the  carpels  are  arranged  so  that 
there  are  as  many  cavities  as  there  are  carpels,  as  if  closed 
carpels  had  come  together,  each  with  its  own  cavity  (Fig. 
Ill,  B).  These  cavities  within  the  ovary  were  long  ago 
called  "  cells,"  and  the  inappropriateness  of  the  term  is 
evident.  Therefore,  some  ovaries  are  said  to  be  one-celled 


FIG.  112.  —  Sections  of  ovules,  showing  outer  (oi)  and  inner  (ii)  integuments,  micro- 
pyle  (m),  nucellus  (n),  and  megaspore  (em)  ;  in  B  the  ovule  is  curved,  and  in  C  the 
stalk  is  curved,  so  that  in  both  cases  the  micropyle  h  turned  towards  the  wall  of 
the  ovary. 

and  some  are  two-  or  more-celled.  It  must  be  noticed  that 
this  does  not  correspond  necessarily  to  the  number  of  carpels, 
for  although  a  simple  pistil  has  a  one-celled  ovary,  a  com- 
pound (syncarpous)  pistil  may  have  either  a  one-celled  ovary 
or  a  several-celled  ovary. 

84.  The  ovule.  —  The  structure  of  the  angiosperm  ovule 
is  essentially  the  same  as  that  of  the  gymnosperm  ovule. 
That  is,  there  are  one  or  two  integuments  investing  the  nu- 
cellus, whose  tip  is  exposed  at  the  micropyle  (Fig.  112). 
In  the  midst  of  the  nucellus  the  usually  solitary  megaspore 
appears,  for,  as  in  Gymnosperms,  although  several .  mega- 
spores  start,  it  is  seldom  that  more  than  one  develops  to  the 
full  size  and  power. 


SPERMATOPHYTES 


141 


The  position  of  the  ovule  within  the  ovary  cavity  has 
certain  features  that  must  be  noted.  The  ordinary  entrance 
to  the  nucellus  is  through  the  micropyle,  and  therefore  the 
position  of  the  micropyle  is  important.  In  some  cases,  the 
ovule  arises  from  the  bottom  of  the  ovary  cavity  (or  near  it) 
and  grows  directly  away  from  the  wall  of  the  ovary,  so  that 
the  micropyle  is  as  far  from  the  wall  as  it  can  be  (Fig.  112,  A), 
which  is  a  relatively  unfavorable  position.  In  most  Angio- 
sperms,  however,  the  ovule  or  its  little  stalk  (funiculus)  curves 
in  growing,  so  that  the  micropyle  is 
brought  relatively  near  the  wall  of  the 
ovary  (Fig.  112,  B  and  C).  That  this 
position  is  a  favorable  one  is  evident 
when  it  is  understood  that  the  pollen 
tube  grows  along  the  wall  of  the  ovary 
and  enters  the  ovule  by  way  of  the 
micropyle.  In  examining  ovules  it 
will  be  found  that  most  of  them  are 
not  straight,  but  are  curved  in  various 
ways,  and  the  curving  means  a  more 
favorable  relation  of  the  micropyle  to 
the  entrance  of  the  pollen  tube. 

85.  The  gametophytes.  —  It  was 
stated  (§  73,  p.  123)  that  among  the  Gymnosperms  the  male 
gametophyte  is  represented  by  a  few  cells  developed  by  the 
microspore  (pollen  grain)  and  remaining  within  it,  and  the 
female  gametophyte  by  a  larger  group  of  cells  developed  by 
the  megaspore  (within  the  ovule)  and  remaining  within  it. 
The  same  statements  are  true  of  the  Angiosperms,  and  the 
gametophytes  are  still  more  reduced  in  the  number  of  cells. 

The  male  gametophyte  (within  the  pollen  grain)  consists 
usually  of  three  cells,  often  represented  only  by  three  nuclei 
(Fig.  113).  One  of  them  is  the  nucleus  associated  with  the 
development  of  the  pollen  tube,  and  hence  is  called  the  tube 
nucleus;  the  other  two  are  the  sperms  (represented  either 


FIG.  113.  —  Pollen  grain 
(microspore)  containing 
the  male  gametophyte 
which  consists  of  three 
cells  or  nuclei ;  the  up- 
permost nucleus  is  the 
tube  nucleus ;  the  two 
cells,  each  containing  a 
nucleus,  are  the  sperms. 


142 


ELEMENTARY   STUDIES   IN   BOTANY 


by  nuclei  or  naked  cells).  It  would  be  hard  to  imagine  a 
gametophyte  reduced  to  lower  terms,  and  it  is  not  at  all 
surprising  that  the  pollen  grain  was  thought  to  be  the  male 
cell,  rather  than  a  spore  containing  a  male  gametophyte.  In 
fact,  no  one  would  have  recognized  these  three  cells  or  nuclei 

as  a  gametophyte,  if 
the  gametophytes  of  the 
Gymnosperms  and  the 
Pteridophytes  had  not 
been  studied. 

The  female  gameto- 
phyte (within  the  mega- 
spore  that  is  in  the 
nucellus)  at  first  consists 
usually  of  eight  nuclei, 
which  become  arranged 
very  definitely  (Fig.  114). 
When  the  megaspore  ger- 
minates to  form  the  ga- 
metophyte, it  ceases  to 
be  a,  spore,  and  is  repre- 
sented only  by  the  encas- 
ing wall  that  surrounds 
the  gametophyte.  The 
cavity  thus  inclosed  is 
called  the  embryo-sac. 
In  other  words,  we  speak 
of  the  megaspore  until 

it  begins  to  germinate,  and  then  we  call  the  same  cavity 
an  embryo-sac.  This  name  was  given  before  there  was 
any  knowledge  of  the  existence  of  a  megaspore  or  a 
female  gametophyte  within  an  ovule,  for  it  was  .seen  that 
the  embryo  appeared  in  a  sac-like  cavity.  Within  this 
embryo-sac  three  of  the  eight  nuclei  become  placed  in  the 
end  of  the  sac  towards  the  micropyle,  and  are  organized  into 


FIG.  114.  —  The  female  gametophyte  of  a  lily, 
having  developed  within  the  megaspore, 
which  is  within  the  nucellus  of  the  ovule ;  in 
the  end  of  the  embryo-sac  (the  name  given 
to  the  megaspore  when  the  gametophyte 
begins  to  develop)  towards  the  micropyle 
(m)  is  a  group  of  three  cells,  one  of  which  is 
the  egg  (e)  ;  at  the  other  end  of  the  sac  is 
another  group  of  three  cells ;  in  the  midst  of 
the  sac  the  two  nuclei  are  seen  which  are  to 
fuse  and  form  the  endosperm  nucleus. 


SPERMATOPHYTES 


143 


a  group  of  three  naked  cells,  one  of  which  is  the  egg.  Three 
other  nuclei  become  placed  at  the  other  end  of  the  sac,  and 
may  remain  as  free  nuclei  or  become 
organized  into  a  group  of  three  cells. 
The  two  remaining  nuclei  behave  in 
a  remarkable  way,  for  they  come  to- 
gether and  fuse  to  form  a  single  large 
nucleus,  which  is  called  the  endosperm 
nucleus  because  it  produces  the  endo- 
sperm, a  tissue  developed  within  the 
embryo-sac  to  nourish  the  embryo.  A 
female  gametophyte  ready  for  fertiliza- 
tion, therefore,  consists  of  seven  cells 
or  nuclei  (Fig.  114)  :  a  group  of  three 
at  the  end  of  the  sac  towards  the  mi- 
cropyle,  one  of  which  is  the  egg ; 
another  group  of  three  at  the  other 
end  of  the  sac ;  and  the  large  endo- 
sperm nucleus  (two  nuclei  fused)  lying 
between. 

86.  Fertilization.  —  The  act  of  fer- 
tilization must  be  preceded  by  pollina-  FlG>  115.  _  Diagram  of 
tion,  which  is  a  notable  feature  of 
Angiosperms.  Among  Angiosperms 
there  is  a  good  deal  of  wind-pollination, 
but  in  addition  to  this  there  is  a  re- 
markable development  of  insect-pollin- 
ation. So  important  and  elaborate  is 
this  relation  between  the  flowers  of 
Angiosperms  and  insects  that  it  will  be 
discussed  in  the  following  chapter.  At 
this  point,  all  that  is  necessary  to  state 
is  that  through  the  agency  of  wind  or  of 
insects  the  pollen  is  carried  from  the  stamens  to  the 
stigmatic  surfaces  of  pistils,  with  of  course  much  loss 


pollen  tubes  penetrating 
the  style  (grains  can 
be  seen  lying  on  the 
stigma) ;  one  of  the 
tubes  has  passed 
through  the  style,  en- 
tered the  ovary  cavity, 
passed  along  the  wall 
of  the  ovary,  entered 
the  micropyle  of  the 
ovule,  penetrated  the 
tip  of  the  nucellus,  and 
discharged  its  two 
sperms  into  the  embryo- 
sac  ;  one  of  the  sperms 
fuses  with  the  egg,  the 
other  with  the  endo- 
sperm nucleus. 


144  ELEMENTARY    STUDIES   IN   BOTANY 

of  pollen  by  the  way.  This  landing  place  of  pollen  in  An- 
giosperms  is  very  different  from  that  in  Gymnosperms.  In 
the  latter  group  the  pollen  reaches  the  tip  of  the  nucellus, 
but  in  the  former  group  it  can  reach  only  the  surface  of  the 
carpel  that  incloses  the  ovules.  This  means  that  in  Gym- 
nosperms the  male  cells  (in  the  pollen  grain)  are  separated 
from  the  egg  only  by  the  tissue  at  the  tip  of  the  nucellus, 
while  in  Angiosperms  the  male  cells  are  separated  from  the 
egg  not  only  by  the  tissue  at  the  tip  of  the  nucellus,  but  also 
by  the  style  and  the  ovary  cavity. 

After  pollination  has  been  accomplished,  therefore,  there 
must  be  an  extensive  development  of  the  pollen  tube  before 
fertilization  can  be  accomplished  (Fig.  115).  A  good  pollen 
grain  lying  on  the  stigmatic  surface  begins  to  send  a  tube  into 
the  style,  and  into  the  tip  of  the  tube  the  two  sperms  pass. 
The  growth  of  the  tube  is  started  by  a  sugary  secretion  of 
the  stigmatic  surface ;  it  continues  its  growth  down  through 
the  style  by  means  of  food  material  supplied  by  the  adjacent 
cells,  enters  the  ovary  cavity,  and  grows  along  its  wall,  enters 
a  favorably  placed  micropyle,  reaches  the  tip  of  the  nucellus, 
grows  on  through  the  tip  of  the  nucellus,  pierces  the  wall  of 
the  embryo-sac,  and  discharges  its  two  sperms,  which  at  last 
have  free  access  to  the  egg. 

Before  fertilization  is  possible,  therefore,  there  must  be 
pollination  and  the  growth  of  a  pollen  tube.  It  is  strange 
that  pollination  and  fertilization  should  ever  be  confused, 
when  they  are  separated  by  such  an  extensive  performance 
as  the  growth  of  the  pollen  tube.  In  some  Angiosperms 
(and  in  many  Gymnosperms)  fertilization  does  not  occur 
until  a  year  after  pollination,  and  the  time  interval  varies 
in  different  plants  between  a  year  and  a  few  hours. 

A  remarkable  situation  is  developed  in  Angiosperms  in 
connection  with  fertilization.  Two  sperms  are  discharged 
into  the  embryo-sac  by  the  pollen  tube,  and  there  is  only  one 
egg.  For  a  long  time  it  was  thought  that  one  sperm  united 


SPERMATOPHYTES 


145 


with  the  egg,  and  that  the  other  sperm  simply  wasted  away, 
accomplishing  nothing.  Now  it  is  known  that  while  one 
sperm  unites  with  the  egg,  the  result  being  a  fertilized  egg, 
the  other  sperm  unites  with  the  endosperm  nucleus,  which 
then  represents  a  case  of  triple  fusion.  This  phenomenon  of 
fertilization  in  the  angiosperm  embryo-sac  has  been  called 

"  double  fertilization."  The  fer- 
tilized egg  forms  the  embryo 
(the  young  sporophyte),  and  the 
fertilized  endosperm  nucleus 
forms  the  endosperm,  a  tissue 
that  feeds  the  embryo. 


FIG.  116.  —  A,  embryo  of 
a  Dicotyledon,  show- 
ing the  terminal  stem 
tip  between  the  two 
cotyledons  (which 
therefore  arise  from 
the  side  of  the  em- 
bryo) ;  B,  an  embryo 
of  a  Monocotyledon, 
showing  the  terminal 
cotyledon,  and  the 
stem  tip  arising  on  one 
side ;  in  both  cases 
the  hypocotyl  is  the 
other  (lower)  end  of 
the  embryo. 


FIG.  117. —  Seed  of  violet,  the  left  figure 
showing  the  hard  seed  coat,  and  the  right 
figure  the  abundant  endosperm  that  sur- 
rounds the  embryo ;  observe  the  regions 
of  the  embryo,  namely,  hypocotyl,  two 
cotyledons,  and  a  minute  plumule  (to  form 
the  stem  with  its  leaves)  between  the 
bases  of  the  cotyledons.  —  After  BAILLON. 


This  double  fertilization  accounts  for  some  things  in  con- 
nection with  seeds  that  were  not  understood  before.  It 
means  that  the  pollen  parent  can  transmit  its  characters  not 
only  to  the  embryo,  but  also  to  the  endosperm.  For  example, 
if  corn  with  red  ears  be  used  as  the  pollen  parent,  and  corn 
with  white  ears  as  the  egg-producing  parent,  it  would  be 
natural  to  expect  a  mixture  of  white  and  red  in  the  ears  of 
the  plant  produced  by  the  embryo.  But  the  fact  had  long 


146 


ELEMENTARY   STUDIES   IN   BOTANY 


been  noted  that  the  mixture  of  white  and  red  also  appeared 
in  the  very  ears  that  had  been  pollinated,  without  waiting 
for  the  embryo  to  develop  a  new  plant.  This  was  a  mystery 
until  double  fertilization  was  discovered,  and  it  was  found  that 
the  red  color  of  the  pollen  parent  was  in  the  endosperm,  and 
had  been  introduced  by  the  sperm  that 
fertilized  the  endosperm  nucleus. 

87.  The  embryo.  —  The  fertilized  egg 
develops  the  embryo,  but  in  Angiosperms 
two  distinct  types  of  embryo  are  developed, 
which  give  names  to  the  great  groups  of 
Angiosperms. 

In  one  type  of  embryo,  the  tip  of  the 
hypocotyl  (see  §  75,  p.  126),  which  is  to 
give  rise  to  the  root,  is  at  one  end  of  the 
embryo,  the  stem  tip  is  at  the  other  end, 
and  the  cotyledons  (see  §  75),  usually  two 
in  number,  develop  on  the  side  of  the 
embryo  just  below  the  stem  tip  (Fig.  116, 
A).  The  Angiosperms  having  this  kind  of 
an  embryo  are  called  Dicotyledons,  and  they 
are  very  much  the  more  numerous  group. 

In  the  other  type  Of  embryo,  the  hy- 
pocotyl tip  is  at  one  end,  the  solitary 
cotyledon  is  at  the  other,  and  the  stem  tip 
develops  on  the  side  of  the  embryo  (Fig.  116,  B).  The 
Angiosperms  having  this  kind  of  embryo  are  called  Mono- 
cotyledons. 

It  must  not  be  supposed  that  the  difference  between  Di- 
cotyledons and  Monocotyledons  depends  upon  the  number  of 
cotyledons,  as  the  names  might  imply,  but  on  the  relative 
position  of  the  stem  tip  and  cotyledon  in  the  two  cases.  For 
example,  a  Dicotyledon,  while  it  usually  has  two  cotyledons, 
may  have  more,  or  it  may  have  only  one  ;  bul  if  the  stem  tip 
is  terminal  rather  than  lateral,  it  is  a  Dicotyledon.  On  the 


FIG.  118.  —  Pod  of 
sweet  pea  burst- 
ing open  to  dis- 
charge its  seeds. 
—  After  GRAY. 


SPERMATOPHYTES 


147 


other  hand,  a  Monocotyledon  is  restricted  to  one  cotyledon 
because  it  is  a  terminal  structure,  but  it  must  be  remembered 
that  an  embryo  with  one  cotyledon  may  belong  to  a  Dicoty- 
ledon. 

88.  The  seed. — The  features  of  a  seed  have  been  described 
under  Gymnosperms  (§  76,  p.  127),  and  they  differ  in  no  es- 
sential way  among  the  Angiosperms.     The  embryo  develops 
to  a  certain  stage,  varying  widely  in  different  plants,  and  then 
passes  into  the  dormant  stage,  probably  due  in  large  measure 
to  the  cutting  off  of  the  water  supply.     Dur- 
ing the  development  of  the  embryo  the  hard 

testa  develops,  protecting  the  delicate  struct- 
ures within  against  the  exposures  of  an 
unfavorable  season,  as  the  cold  of  winter, 
dryness,  etc.  (Fig.  117). 

The  seeds  of  Angiosperms  differ  widely  as 
to  the  amount  of  endosperm  left  by  the  em- 
bryo when  it  becomes  dormant.  The  endo- 
sperm in  a  seed,  therefore,  may  vary  from 
a  great  deal  (Fig.  117)  to  none  at  all.  For 
example,  in  the  seeds  ("  grains  ")  of  cereals 
(wheat,  corn,  rice,  etc.)  a  great  amount  of 
endosperm  is  left,  and  the  world  gets  much 
of  its  food  from  this  source ;  while  in  peas 
and  beans  no  endosperm  is  left,  but  the  coty- 
ledons have  stored  up  the  food  supply  taken 
from  the  destroyed  endosperm  and  have  become  bulky,  so 
that  in  this  case  we  use  the  cotyledons  for  food  instead 
of  the  endosperm  directly. 

89.  The   fruit.  —  While   the   seeds   of  Angiosperms    are 
ripening,  changes  take  place  also  in  structures  outside  the 
seed.     For  example,  the  ovary  wall  may  change  and  become 
a  hard  or  parchment-like  seed-vessel,  as  in  peas  and  beans, 
whose  seed-vessels  are  called  pods  (Figs.  118  and  119).     In 
other  cases,  the  whole  ovary  may  become  a  thin-skinned 


FIG.  119.  — Pod  of 
iris  ("three- 
celled")  burst- 
ing open. — 
After  GRAY. 


148  ELEMENTARY    STUDIES   IN   BOTANY 

pulpy  mass  in  which  the  seeds  are  imbedded,  as  in  the  grape, 
currant,  gooseberry,  tomato,  etc.,  all  of  which  are  berries. 
In  still  other  cases,  the  ovary  wall  may  ripen  into  two  layers, 
the  inner  one  being  very  hard  and  the  outer  one  being  fleshy, 
as  in  the  peach,  plum,  cherry,  etc.,  which  are  called  stone-fruits 
(Fig.  120).  Sometimes  the  changes  extend  beyond  the 
ovary.  For  example,  the  cup-like  base  of  the  flower  sur- 
rounding the  ovary  may  become  fleshy,  as  in  the  apple  and 
pear,  in  which  the  ovary  is  represented  by  the  "  core  "  con- 
taining the  seeds  (Fig.  121).  An  extreme  case  is  the  pine- 
apple, in  which  a  whole  flower  cluster 
has  become  an  enlarged  fleshy  mass,  in- 
cluding the  axis  and  the  bracts  (Fig. 
122). 

All  of  these  changes  outside  the  seed 
result  in  what  is  called  the  fruit.  It 
is  evident  that  "  fruit  "  is  a  very 
indefinite  thing.  It  may  be  dry  or 

FIG.    120.  —  Section    of    a  .  J 

peach,  showing  pulp  and     fleshy,  and   it  may  include    only  the 
<H3,     ovary,  or  it  may  extend  to  the  base 


and  inclosing  the  seed     of    ^he    flower,   or   it   may  involve   a 

(kernel).  —  After  GRAY. 

whole  cluster  of  flowers. 

90.  Summary.  —  The  Angiosperms  are  far  more  varied 
and  abundant  than  are  the  Gymnosperms,  and  constitute 
the  conspicuous  vegetation  of  the  land  surface,  and  also  the 
vegetation  of  greatest  importance  to  man.  Three  features  of 
the  group  stand  out  conspicuously  in  contrast  with  Gym- 
nosperms. 

The  first  feature  is  the  inclosed  ovule,  the  inclosing  struct- 
ure being  the  carpel.  This  means  that  the  pollen  grains,  con- 
taining the  male  gametophytes,  cannot  reach  the  ovule,  but 
are  received  by  a  special  region  of  the  surface  of  the  carpel 
(the  stigma)  .  This  means,  further,  that  the  pollen  tube  must 
traverse  the  style,  enter  the  cavity  of  the  ovary,  reach  the 
tip  of  an  ovule  (the  position  for  the  pollen  grain  in  Gymno- 


FIG.   121.  —  Longitudinal  and  cross-sections  of  an  apple,  showing  the  "five-celled 
ovary  (core)  imbedded  in  the  fleshy  cup  of  the  flower. 


FIG.  122.  —  Pineapple,  showing  the  whole  flower  cluster  becoming  a  "fruit."  —  Pho- 
tograph by  LAND  in  Southern  Mexico. 

11  149 


150  ELEMENTARY   STUDIES   IN   BOTANY 

sperms),  and  then  penetrate  the  tip  of  the  ovule  until  the  egg 
is  reached. 

The  second  feature  is  the  appearance  of  the  flower,  which 
differs  from  a  strobilus  in  having  another  set  of  members 
added  to  the  sporophylls,  and  this  set  (perianth)  is  generally 
differentiated  into  sepals  (calyx)  and  petals  (corolla). 

The  third  feature  is  related  closely  to  the  second,  for  it  is 
the  development  of  insect-pollination.  Many  Angiosperms 
retain  the  old  method  of  wind-pollination,  but  insect-pol- 
lination is  a  conspicuous  feature  of  the  group,  and  it  is  as- 
sociated with  the  remarkably  diversified  development  of 
flowers. 

In  addition  to  these  conspicuous  features  of  Angiosperms, 
there  are  two  others  that  should  be  remembered.  The 
gametophytes  are  reduced  to  their  lowest  terms,  and  two 
kinds  of  embryo  are  formed  (dicotyledonous  and  monocotylc- 
donous) . 


CHAPTER  IX 
THE  FLOWER  AND   INSECT-POLLINATION 

91.  Evolution  of  the  flower.  —  Perhaps  the  most  con- 
spicuous feature  of  Angiosperms  is  the  endless  variety  of 
flowers.     In  fact,  the  130,000  different  kinds  of  Angiosperms 
are  largely  distinguished  by  their  flowers,  which  means  that 
there  are  many  thousands  of  different  kinds  of  flowers.     In 
an  elementary  book,   therefore,   it  is  possible  to   consider 
only  flowers  in  general.     We  recognize  the  fact  that  flowers, 
starting  with  the  strobilus  condition,  have  changed  in  many 
directions,  and  it  is  not  difficult  to  recognize  some  of  the 
conspicuous   directions.     With   these   in  mind,   any   flower 
examined  will  show  to  the  observer  the  amount  of  progress 
it  has  made,  and  the  general  direction  it  has  taken. 

92.  Primitive  flowers.  —  If  changes  in  flowers  are  to  be 
noted,  some  starting  point  must  be  established.     It  is  natural 
to  suppose  that  the  most  primitive  flowers  are  those  nearest 
the  strobilus  condition.     This  means  that  the  sporophylls 
(stamens  and  carpels)  are  numerous,  arising  from  a  more  or 
less  elongated  axis ;  that  they  are  entirely  separate  from  one 
another ;    and  that  beneath  them  there  arises  the  perianth 
that  distinguishes  a  flower  from  a  strobilus.     This  perianth 
consists  of  members  that  are  entirely  separate  from  one  an- 
other, and  these  members  are  all  alike,  forming  more  or  less 
of  a  rosette  beneath  or  around  the  sporophylls.     Probably 
in  the  most  primitive  flowers  the  perianth  consisted  of  bract- 
like  members,  neither  delicate  in  texture  nor  brightly  colored. 

It  is  from  some  such  condition  that  the  changes  in  flowers 
started,  and  the  most  conspicuous  changes  are  indicated  in 
the  five  following  sections. 

151 


152  ELEMENTARY    STUDIES   IN   BOTANY 

93.  The  perianth.  —  If  the  members  of  the  perianth  are 
all  alike  in  primitive  flowers,  they  have  not  remained  so  in 
most  flowers.     In  general,  they  have  become  differentiated 
into  two  very  different  sets  (Figs.  101  and  108),  the  calyx  and 
the  corolla  (§  81,  p.  131 ) .     These  sets  differ  not  only  in  appear- 
ance, but  also  in  the  use  to  which  they  are  put.     The  sepals 
(calyx)  are  usually  leaf-like  in  texture  and  color,  and  protect 
the  more  delicate  inner  members  while  in  the  bud  condition. 
The  petals  (corolla)  are  usually  larger,  more  delicate  in  text- 
ure, and  not  green,  their  color  being  called  the  color  of  the 
flower.     Such  petals  are  associated  in  some  way  with  the 
visits  of  insects,  which  will  be  considered  later. 

Almost  every  kind  of  exception  to  this  general  statement 
can  be  found.  For  example,  in  the  lily,  the  members  of  the 
perianth  are  in  two  sets,  but  they  are  both  petal-like  in 
texture  and  color,  so  that  they  can  be  distinguished  only  by 
their  relative  positions  (Fig.  123).  In  some  flowers  the  petals 
have  disappeared,  and  the  sepals  may  have  the  color  and 
texture  of  petals.  Flowers  without  petals  are  said  to  be 
apetalous  ("  without  petals  "). 

In  spite  of  exceptions  that  may  obscure  the  fact,  the  most 
general  tendency  of  flowers  is  to  develop  the  perianth  as  two 
distinct  sets  of  members. 

94.  Definite  numbers.  —  In  the  more  primitive  flowers, 
the  members  are  indefinite  in  number,  for  they  are  produced 
upon  a  more  or  less  elongated  axis,  as  in  a  strobilus.     In  the 
majority  of  flowers,  however,  this  axis  does  not  elongate, 
but  remains  short  and  generally  broadens  at  the  tip.     In 
such   cases,   the   flower  members   are   produced  upon   this 
broadened  tip  (receptacle),  and  cannot  be  indefinite  in  num- 
ber, for  the  space  is  limited.     As  a  consequence,  they  appear  in 
four  circles,  and  each  circle  has  a  definite  number  of  members. 

It  is  remarkable  how  constant  the  numbers  are  in  the  two 
great  groups  of  Angiosperms.  In  the  Dicotyledons  (§87, 
p.  146)  with  definite  numbers,  the  prevailing  number  is  five, 


THE   FLOWER  AND   INSECT-POLLINATION        153 

and  a  much  less  frequent  number  is  four.     In  the  Mono- 
cotyledons (§  87)  with  definite  numbers,  the  prevailing  num- 


FIG.  123.  —  Dogtooth  violet  (lily  family),  with  parts  of  the  perianth  all  alike,  and 
hypogynous  flowers. 

ber  is  three.     This  fact  is  a  convenience  in  recognizing  these 
two  groups  without  being  compelled  to  examine  the  embryo. 


154  ELEMENTARY   STUDIES   IN   BOTANY 

For  example,  if  the  members  of  a  flower  are  in  sets  of  five 
or  four,  the  plant  is  a  Dicotyledon ;  if  they  are  in  sets  of 
three,  the  plant  is  a  Monocotyledon.  This  distinction  does 
not  hold  in  all  cases,  but  it  may  be  depended  upon  in  the 
majority  of  the  ordinary  flowers. 

It  is  very  common  for  the  stamen  set  to  be  doubled,  so 
that  the  flower  of  a  Dicotyledon  may  have  five  sepals,  five 
petals,  ten  stamens,  and  five  carpels;  and  the  flower  of  a 
Monocotyledon  may  have  three  sepals,  three  petals,  six 
stamens,  and  three  carpels.  On  the  other  hand,  in  the  most 
advanced  families  of  Dicotyledons  the  carpels  become  re- 
duced in  number.  For  example,  in  the  most  advanced  family 
of  Angiosperms,  and  therefore  the  highest  of  all  plants  (the 
family  to  which  sunflowers,  goldenrods,  asters,  dandelions, 
etc.,  belong),  the  flower  has  five  sepals,  five  petals,  five 
stamens,  and  two  carpels. 

An  important  fact  to  notice  is  that  all  four  members  of  a 
flower  may  not  have  advanced  together,  so  that  some  of  the 
members  may  have  reached  definite  numbers,  while  the  other 
members  still  have  indefinite  numbers.  For  example,  the 
flower  of  the  ordinary  buttercup  has  five  sepals  and  five 
petals,  but  it  has  an  indefinite  number  of  stamens  and  carpels. 
This  is  one  of  the  facts  that  indicates  that  a  buttercup  is  a 
much  more  primitive  flower  than  an  aster. 

95.  United  petals.  —  It  is  a  very  general  tendency  in 
flowers  for  any  set  of  members  to  develop  altogether,  and 
thus  appear  as  if  they  had  been  united.  It  should  be  em- 
phasized that  they  are  not  united  in  the  sense  that  they  ever 
were  separate,  but  that  developing  all  together,  they  appear 
as  if  they  had  been  united.  There  are  all  degrees  of  this 
apparent  union,  from  an  appearance  of  union  only  at  base 
to  an  appearance  of  union  throughout. 

It  is  so  common  for  carpels  to  behave  in  this  way,  resulting 
in  "  compound  pistils,"  that  it  seems  rather  exceptional  when 
this  is  not  the  case  (Fig.  110),  Such  behavior  on  the  part 


THE   FLOWER  AND  INSECT-POLLINATION        155 

of  the  stamens  is  much  less  common  (Fig.  108) ;  and  while 
it  is  much  more  common  in  the  case  of  the  sepals,  it  is  quite 
irregular. 

It  is  petals,  however,  that  deserve  special  attention,  for 
their  growth  in  common  or  separately  is  a  regular  feature  of 
great  groups.  The  various  forms  that  these  so-called  "  united 
petals  "  assume  are  well  known  to  all  who  notice  flowers,  as 
the  funnel-shaped  corolla  of  the  morning  glory,  the  bell- 
shaped  corolla  of  the  bell-flower,  the  nearly  wheel-shaped 
corolla  of  the  potato  or  tomato  flower,  the  tubular  corolla 
of  the  coral  honeysuckle,  etc.  (Figs.  102  and  103).  A  corolla  in 
this  condition  is  called  sympetalous  (§  81,  p.  133).  So  constant 
a  feature  is  it  of  the  families  in  which  it  occurs,  that  it  gives 
name  to  one  of  the  two  great  groups  of  Dicotyledons,  the 
Sympetalce.  The  Sympetalse  include  all  the  higher  families 
of  the  Dicotyledons,  and  in  distinction  from  them,  all  the 
Dicotyledons  whose  flowers  are  not  sympetalous  are  called 
Archichlamydece,  a  name  which  means  "  primitive  perianth," 
and  is  intended  to  include  not  only  flowers  that  have  the 
petals  separate  (polypetalous),  but  also  those  without  petals 
and  even  without  a  perianth. 

In  this  connection  it  may  be  pointed  out  that  there  are 
three  great  groups  of  Angiosperms  to  remember :  the  Mono- 
cotyledons and  the  two  groups  of  Dicotyledons.  They  are 
very  easy  to  distinguish  ordinarily  by  their  flowers,  for  if  a 
flower  has  its  members  in  threes,  it  is  almost  certain  to  belong 
to  a  Monocotyledon ;  if  it  has  its  members  in  fives  or  fours 
and  its  petals  are  separate,  it  belongs  to  the  Archichlamydeae ; 
if  the  flower  parts  are  in  fives  or  fours  and  the  corolla  is  sym- 
petalous, it  is  one  of  the  Sympetalae. 

96.  Union  of  two  or  more  sets.  —  Not  only  do  the  members 
of  a  single  set  often  appear  united  in  a  flower,  but  two  or  more 
sets  may  grow  together  more  or  less  completely.  It  has  been 
mentioned  (§  82,  p.  136)  that  in  the  case  of  sympetalous  corollas 
it  is  usual  to  have  the  stamens  develop  in  common  with  themr 


156  ELEMENTARY    STUDIES    IN   BOTANY 

so  that  they  appear  to  grow  from  the  tube  of  the  corolla 
(Fig.  102).  In  the  orchids,  the  stamen  and  carpel  sets  grow 
together  so  completely  that  they  form  a  very  unusual  looking 
structure  in  the  midst  of  the  flower.  The  most  important 
conditions  of  this  kind,  however,  appear  under  the  following 
definitions : 

When  the  sepals,  petals,  and  stamens  all  arise  from  under- 
neath the  pistil  or  pistils,  so  that  one  looks  within  the  flower 
for  the  ovary  (Figs.  101,  123,  and  124,  A),  the  flower  is  said 
to  be  hypogynous  ("  under  the  pistil  ")•  When  the  three 


FIG.  124.  —  A,  hypogynous  flower  (Potentittd)  ;  B,  perigynous  flower  (apple).  —  After 
ENGLER  and  PRANTL. 

outer  sets  grow  together  and  form  a  cup-like  structure  about 
the  pistil  or  pistils,  and  from  the  rim  of  this  cup  the  sepals, 
petals,  and  stamens  seem  to  arise,  as  in  roses  and  apples 
(Fig.  124,  B),  the  flower  is  said  to  be  perigynous  ("  around 
the  pistil  ")•  When  all  four  sets  grow  together  in  such  a 
way  that  the  sepals,  petals,  and  stamens  seem  to  arise  from 
the  top  of  the  ovary,  so  that  one  looks  beneath  the  flower  for 
the  ovary,  as  in  amaryllis  (Fig.  125)  and  iris  (Fig.  127),  the 
flower  is  said  to  be  epigynous  ("-upon  the  pistil  ").  Hypogy- 
nous flowers  represent  the  most  primitive  condition  of  the 
flower,  while  epigynous  flowers  are  characteristic  of  all  the 
higher  families  of  Angiosperms. 

97.   Irregularity.  —  In  some  flowers  the  members  of  a  set 


THE   FLOWER  AND   INSECT-POLLINATION        157 


are  not  all  alike,  and  this  tendency  is  chiefly  noted  in  connec- 
tion with  the  corolla.  Attention  has  been  called  to  the  irregu- 
larity of  such  flowers  as  the  sweet  pea  and  the  snapdragon 
(§  81,  p.  133),  the  two  kinds  of  irregularity  they  represent  being 
characteristic  of  certain  large  families  (Fig.  103,  C,  D,  and  E). 
In  addition  to  these,  attention  should  be 
called  to  the  irregularities  called  spurs 
(Fig.  103,  E),  which  are  conspicuous 
in  orchids  (Fig.  128),  larkspurs,  etc.,  and 


FIG.  125.  —  Snow- 
flake  (amaryllis 
family),  with 
epigynous  flow- 
ers.  —  After 
STRASBURGER. 


FIG.  126.  —  Rose  acacia:  A,  keel  projecting  from  calyx 
(the  other  petals  removed) ;  B,  protrusion  of  tip  of 
style  when  keel  is  depressed ;  C,  section  showing  posi- 
tion of  parts  within  the  keel.  —  After  GRAY. 


to  sacs  or  pouches,  such  as  appear  in  the  lady  slippers. 
These  spurs  and  sacs  are  always  associated  with  the  secre- 
tion of  nectar,  for  which  many  insects  visit  flowers. 

98.  General  statement.  —  In  the  preceding  sections,  the 
prominent  departures  from  the  condition  of  the  primitive  flower 
have  been  noted.  It  should  be  understood  that  these  depart- 
ures occur  in  all  sorts  of  combinations,  and  it  is  the  varying 
combinations  that  make  the  conspicuous  differences  among 


158 


ELEMENTARY   STUDIES    IN   BOTANY 


flowers.  A  flower  that  has  an  indefinite  number  of  members, 
and  that  is  polypetalous,  hypogynous,  and  regular,  has  a 
combination  of  characters  that  puts  it  low  in  the  scale  of 
Angiosperms.  On  the  other  hand,  a  flower  with  a  definite 
number  of  members,  and  that  is  sympetalous,  epigynous, 

and  irregular,  has  a  com- 
bination of  characters  that 
ranks  it  very  high.  By 
observing  the  combina- 
tions in  the  flower,  the 
relative  positions  of  the 
flowering  plants  may  be 
estimated. 

99.  Pollination  by  in- 
sects. —  It  has  been  stated 
(§  86,  p.  143)  that  the  pre- 
vailing method  of  pollina- 
tion among  Angiosperms 
is  the  use  of  insects  as  the 
agents  of  transfer.  The 
method  of  transfer  by 
means  of  the  wind,  as 

FIG.   127.  —  Longitudinal    section    of  an  iris  „  /~i  j 

flower,  showing    a    stamen    between    the        among  UymnOSpermS  and 
drooping  petal   and    the  petal-like  style ; 


the  stigmatic  shelf  is  seen  at  the  top  of  the 
style  above  the  stamen;  the  nectar  pit  is 
at  the  junction  of  petal  and  stamen; 
observe  the  section  of  the  ovary,  whose 
position  shows  that  the  flower  is  epigy- 
nous. —  After  GRAY. 


many  Angiosperms,  is 
wasteful,  in  the  sense  that 
there  must  be  a  great 
amount  of  pollen  pro- 
duced in  order  that  a  little 

of  it  may  be  sure  to  reach  the  right  spots.  When  insects 
carry  pollen  directly  from  one  plant  to  another,  pollination 
becomes  so  definite  a  process  that  a  comparatively  small 
amount  of  pollen  is  sufficient  to  insure  pollination. 

The  transfer  of  pollen  from  the  stamen  to  the  pistil  of  the 
same  flower  is  called  self-pollination,  while  transfer  to  the 
pistil  of  another  flower  is  called  cross-pollination.  The 


THE   FLOWER  AND    INSECT-POLLINATION        159 

"  other  flower  "  may  be  upon  the  same  plant  or  upon  a  dif- 
ferent plant,  but  the  cross-pollination  that  is  significant  is 
that  which  involves  two  distinct  plants.  Since  flowers  are 
very  commonly  arranged  to  secure  cross-pollination,  it  must 
be  of  more  advantage  to  plants  in  general  than  self-pollina- 
tion. 

This  relation  between  flowers  and  insects  is  mutually 
helpful,  for  the  flower  secures  pollination  and  the  insect 
secures  food.  The  food  supplied  by  the  flower  is  either 
nectar,  a  sweet  secretion  often  wrongly  called  "  honey,"  or 
pollen.  The  insects  that  visit  flowers  may  be  grouped  as 
nectar-feeders,  represented  by  moths  and  butterflies,  and 
pollen-feeders,  represented  by  bees  and  wasps.  The  pres- 
ence of  these  supplies  of  food  is  made  known  to  the  insect  by 
the  display  of  color,  by  odor,  or  by  form.  Just  what  attracts 
different  insects  is  not  always  clear,  but  color,  odor,  and 
characteristic  forms  belong  to  flowers  visited  by  insects,  so 
that  it  seems  safe  to  conclude  that  by  these  features  the  in- 
sects recognize  their  feeding  ground. 

The  relation  between  flowers  and  insects  is  most  striking 
in  those  flowers  arranged  for  cross-pollination.  This  ar- 
rangement involves  both  the  hindrance  of  self-pollination 
and  the  securing  of  cross-pollination,  and  each  kind  of  cross- 
pollinating  flower  has  solved  these  problems  in  its  own  way. 
A  few  examples  will  be  given,  to  suggest  the  kinds  of  arrange- 
ments to  be  looked  for,  but  the  student  should  examine  as 
many  cross-pollinating  flowers  as  possible,  and  try  to  deter- 
mine how  self-pollination  is  hindered  and  how  cross-pollination 
is  secured. 

In  those  plants  that  have  staminate  and  pistillate  flowers 
on  different  individuals,  the  case  is  clear,  for  self-pollination 
is  effectually  prevented  by  the  absence  of  stamens  from 
flowers  with  pistils.  However,  in  such  cases,  the  wind  is  as 
apt  to  be  the  agent  of  pollination  as  insects. 

The  most  difficult  situation  is  where  stamens  and  pistils 


160  ELEMENTARY    STUDIES   IN   BOTANY 

are  associated  in  the  same  flower,  and  the  pollen  is  ready  for 
shedding  and  the  stigma  ready  to  receive  at  the  same  time. 
In  such  a  case  nothing  can  prevent  self-pollination  except 
some  mechanical  hindrance  that  makes  it  unlikely  that  the 
pollen  will  reach  the  stigma.  It  is  this  situation  that  has 
resulted  in  many  of  the  irregularities  and  striking  forms  of 
flowers,  so  that  such  flowers  are  among  those  most  prized 
in  cultivation.  Three  notable  examples  will  serve  as  illus- 
trations. 

The  sweet  pea  and  its  allies  have  what  are  called  "  butter- 
fly-shaped "  flowers.  Two  of  the  petals  together  form  a 
boat-shaped  structure  (keel)  which  encloses  the  several 
stamens  and  the  simple  pistil  (Fig.  126).  The  stigmatic 
surface  is  on  the  top  of  the  style  and  projects  beyond  the 
anthers,  whose  shed  pollen  lodges  on  a  hairy  zone  of  the  style 
below  the  stigma.  The  projecting  keel  is  the  natural  land- 
ing place  for  a  bee  visiting  the  flower;  and  this  keel  is  so 
attached  that  the  weight  of  the  insect  depresses  it.  This 
depression  of  the  keel  causes  the  tip  of  the  style  to  emerge 
and  to  strike  the  body  of  the  insect.  It  is  a  glancing  blow, 
so  that  after  the  tip  has  struck  the  insect,  the  surface  of  the 
style  is  also  rubbed  against  its  body,  brushing  the  lodged 
pollen  on  to  the  insect.  At  the  next  flower  visited,  the  stigma 
strikes  the  pollen  brushed  off  in  the  previous  flower,  and  then 
a  new  supply  of  pollen  is  brushed  from  the  style.  In  this 
way,  each  flower  visited  receives  pollen  from  the  preceding 
one,  and  sends  pollen  to  the  next  one.  Of  course,  there  are 
large  elements  of  chance  in  such  a  performance,  but  certainly 
self-pollination  is  fairly  well  guarded  against,  and  cross- 
pollination  is  very  likely  to  be  secured. 

In  the  iris,  often  called  "  flag,"  each  stamen  is  in  a  kind  of 
pocket  between  a  petal  and  a  petal-like  style  (Fig.  127).  The 
stigmatic  surface  is  on  the  top  of  a  flap  or  shelf  which  extends 
from  the  style  as  a  roof  over  the  pocket.  With  the  stamen 
beneath  this  shelf  and  the  stigmatic  surface  on  top,  it  is  clear 


THE   FLOWER  AND   INSECT-POLLINATION        161 


that  self-pollination  must  be  very  unlikely.  The  nectar  is 
in  a  little  pit  at  the  bottom  of  the  pocket.  As  the  insect 
crowds  its  way  into  the  nar- 
rowing pocket,  its  body  is 
dusted  by  the  pollen ;  and 
when  it  visits  the  next  flower, 
and  pushes  aside  the  stigmatic 
shelf,  it  is  likely  to  deposit 
upon  it  some  of  the  pollen 
obtained  from  a  previously 
visited  flower. 

The  orchids  are  most  re- 
markable in  their  arrange- 
ment for  insect-pollination. 
In  fact,  each  kind  of  orchid 
is  usually  so  adjusted  to  some 
particular  kind  of  insect  that 
no  other  insect  can  secure  the 
nectar  or  carry  off  the  pollen. 
There  are  two  pollen  sacs,  and 
the  pollen  grains  cling  to- 
gether in  a  mass,  which  is 
pulled  out  of  the  sac  bodily. 
A  common  arrangement  is  as 
follows  (Fig.  128).  Each  of 
the  elongated  pollen  masses 
terminates  below  in  a  stalk 
that  ends  in  a  sticky  disk  or 
button,  and  between  these  two 
buttons  there  extends  the 
concave  stigmatic  surface,  at 
the  bottom  of  which  is  the 
opening  into  the  long  tube-like  spur  containing  the  nectar. 
Such  a  flower  is  adjusted  to  the  visits  of  a  large  moth,  with 
a  long  sucking-tube  ("  proboscis  ")  that  can  reach  the  bottom 


FIG.  128.  —  Flower  of  an  orchid  (Habe- 
naria)  :  A,  complete  flower,  showing 
three  broad  sepals,  three  narrower 
petals  (the  lowest  one  forming  the 
long  lip  and  the  much  longer  spur 
which  extends  to  the  bottom  of  the 
figure),  two  pollen-sacs,  between  which 
extends  the  concave  stigmatic  surface 
(at  the  bottom  of  which  the  opening 
to  the  spur  is  seen)  ;  B,  more  enlarged 
view  of  pollen-sacs  with  their  sticky 
buttons  and  the  stigmatic  surface 
stretching  between  ;  C,  a  pollen-mass 
removed ;  D,  a  button  enlarged.  — 
After  GRAY. 


162  ELEMENTARY    STUDIES   IN   BOTANY 

of  the  spur.  As  the  moth  thrusts  its  proboscis  into  the  tube, 
its  broad  head  (against  the  stigmatic  surface)  is  pressed 
against  the  sticky  button  on  each  side,  so  that  when  it  flies 
away  these  buttons  stick  to  its  head  and  the  pollen  masses 
are  torn  out.  When  the  next  flower  is  visited,  and  the  head 
of  the  moth  is  pressed  against  the  sticky  stigmatic  surface, 
the  pollen  masses  from  the  previously  visited  flower  are 
thrust  against  it  and  are  left  there. 


FIG.  129.  —  Flower  of  figwort  (Scrophularia)  :  A,  stigma,  in  position  to  receive  pollen; 
B,  section  of  A,  showing  stamens  curved  back  in  tube  of  corolla  ;  C,  later  condition, 
with  style  collapsed  and  stigma  not  in  a  condition  to  receive  pollen,  but  the  anthers 
brought  up  in  position  for  shedding.  —  After  GRAY. 

A  very  common  arrangement  to  prevent  self-pollination 
in  flowers  containing  both  stamens  and  pistils  is  for  the  pollen 
and  the  stigma  to  mature  at  different  times  ;  that  is,  when  the 
pollen  is  being  shed,  the  stigma  is  not  ready  to  receive ;  or 
when  the  stigma  is  ready  to  receive,  the  pollen  is  not  ready  to 
be  shed.  The  two  following  examples  will  serve  to  illustrate. 

When  the  flowers  of  the  ordinary  figwort  open,  the  style 
bearing  the  stigma  at  its  tip  is  found  protruding  from  the 
urn-like  flower,  while  the  four  stamens  are  curved  down  into 
the  tube,  and  are  not  ready  to  shed  their  pollen  (Fig.  129). 
At  some  later  time,  the  style  bearing  the  stigma  wilts,  and  the 
stamens  straighten  up  and  protrude  from  the  tube.  In  this 


THE   FLOWER  AND   INSECT-POLLINATION        163 

way,  first  the  receptive  stigma  and  afterward  the  shedding 
pollen  sacs  occupy  the  same  position.  A  visiting  insect  will 
probably  find  flowers  in  both  conditions,  and  in  striking 
against  protruding  pollen  sacs  in  some  flowers  and  protruding 
stigmas  in  others,  it  carries  pollen  from  one  flower  to  another. 
In  this  case,  the  stigma  is  ready  first ;  but  it  is  more  common 
for  the  pollen  to  be  ready  first,  as  in  wild  geraniums,  willow 
herb  ("  fire  weed  "),  etc.  In  the  latter  case,  when  the  flower 
opens,  the  eight  shedding  stamens  project  prominently, 
while  the  style  is  sharply  curved  downward  and  backward, 


FIG.  130.  —  Flower  of  willow  herb  (Epilobiuni) :  A,  anthers  in  position  for  shedding  and 
style  curved  downward ;  B,  later  condition,  with  anthers  empty  and  stigmatic 
lobes  of  style  in  position  for  receiving  pollen.  —  After  GRAY. 

carrying  the  stigmatic  surface  well  out  of  the  way  (Fig.  130). 
Later,  the  stamens  bend  away  and  the  style  straightens  up  and 
exposes  the  stigma.  The  result  of  insect  visits  is  the  same 
as  described  for  the  figwort. 

Still  another  arrangement  is  not  very  common,  but  none 
the  less  interesting.  The  stamens  and  pistils  are  together 
in  the  flower,  but  there  are  usually  two  forms  of  flowers.  In 
the  little  plant  called  "  innocents  "  or  "  bluets,"  for  example 
(Fig.  131),  one  kind  of  flower  has  short  stamens  included  in 
the  tube,  while  the  style  is  long  and  projecting.  In  the  other 
kind  of  flower  the  stamens  are  long  and  projecting,  while  the 
style  is  short  and  included  in  the  tube.  There  is  some  dif- 
ference between  the  pollen  produced  by  the  long  stamens 


164 


ELEMENTARY    STUDIES    IN   BOTANY 


and  that  produced  by  the  short  stamens,  for  the  pollen  from 
the  long  stamens  is  more  effective  on  the  long  styles  than 
it  is  on  the  short  ones,  and  vice  versa.  This  means  that 
the  pollen  of  either  kind  of  flower  is  not  effective  on  the  style 
of  the  same  flower.  The  body  of  the  visiting  insect  fills  the 
tube  of  the  small  corolla  and  projects  above  it.  In  visiting 
both  kinds  of  flowers,  one  region  of  the  body  receives  a 


FIG.  131.  —  Flowers  of  innocence  (Houstonia)  :    A,  form  with  short  stamens  and  long 
style ;    B,  form  with  long  stamens  and  short  style.  —  After  GRAY. 

band  of  pollen  from  the  short  stamens,  and  another  region  of 
the  body  receives  a  band  of  pollen  from  the  long  stamens. 
In  this  way  the  insect  is  soon  carrying  about  two  bands  of 
pollen,  which  come  in  contact  with  the  stigmas  of  the  short 
styles  and  of  the  long  styles. 

100.  Pollination  and  plant-breeding.  —  The  purpose  of 
practical  plant-breeding  is  to  improve  the  old  races  of  useful 
plants  and  to  produce  new  ones.  In  this  work  advantage  is 
taken  of  pollination  to  produce  certain  results.  Probably  the 


THE    FLOWER  AND   INSECT-POLLINATION        165 

most  common  method  of  producing  new  and  desirable  forms- 
is  to  "  cross  "  two  different  kinds  of  plants;  that  is,  to  take 
the  pollen  of  one  kind  and  apply  it  to  the  stigma  of  another 
kind.  This  is  artificial  pollination,  in  the  sense  that  the  plant- 
breeder  is  the  agent  of  transfer,  but  such  crosses  are  occurring 
constantly  in  nature.  The  plant-breeder,  however,  makes  a 
cross  for  a  definite  purpose,  while  crosses  in  nature  are  in- 
definite and  matters  of  chance.  The  plant  that  is  produced 
by  crossing  parent  plants  of  different  kinds  is  a  hybrid.  The 
purpose  of  the  plant-breeder  in  producing  hybrids  is  to  get 
in  a  single  plant  a  combination  of  desirable  qualities  belong- 
ing to  the  two  parents.  It  must  not  be  supposed  that  every 
hybrid  shows  the  desired  combination,  for  usually  only  one 
individual  out  of  thousands  will  show  it.  For  example,  if  a 
race  of  wheat  is  found  to  be  very  resistant  to  dry  weather, 
this  feature  would  be  rsgarded  as  a  very  desirable  one.  This 
valuable  "  drought-resistant  "  character,  however,  might  be 
associated  with  a  grain  of  poor  quality,  so  that  this  kind  of 
wheat  could  not  serve  our  purpose.  One  method  of  pro- 
cedure in  such  a  case  would  be  to  cross  a  wheat  of  good  qual- 
ity with  the  drought-resistant  wheat,  in  the  hope  that  among 
the  hybrids  thus  produced,  some  one  of  them  would  have  the 
desired  combination  of  good  quality  and  drought-resistance. 
If  this  could  be  the  case,  the  desirable  hybrid  would  be  propa- 
gated, this  time  cross-pollination  being  guarded  against, 
and  the  seed  multiplied  for  use.  The  use  of  hybrids  in 
plant-breeding,  therefore,  is  to  secure  desired  combinations 
of  characters,  and  the  securing  of  hybrids  is  by  artificial 
pollination. 

101 .  Summary. — The  evolution  of  the  flower  has  proceeded 
in  many  directions,  but  there  are  certain  general  tendencies  that 
can  be  kept  in  mind.  The  -perianth  is  generally  differentiated 
into  two  sets,  the  sepals  and  the  petals,  and  the  latter  usually 
constitute  the  conspicuous  feature  of  the  flower.  There  is 
also  a  tendency  to  shorten  the  receptacle,  so  that  the  num- 
12 


166  ELEMENTARY   STUDIES   IN   BOTANY 

ber  of  each  set  is  definite,  the  prevailing  number  of  flower 
parts  among  Dicotyledons  being  five  or  four,  and  among 
Monocotyledons  three.  There  is  also  a  strong  tendency  for 
the  members  of  any  set  to  develop  together  so  as  to  appear 
united.  This  is  most  common  in  the  case  of  carpels,  so  that 
a  pistil  most  frequently  consists  of  more  than  one  carpel,  but 
it  is  most  regular  in  the  case  of  petals,  characterizing  one  of 
the  three  great  groups  of  Angiosperms  (Sympetalse) .  There 
is  also  a  tendency  for  two  or  more  sets  to  develop  together 
so  as  to  appear  united,  the  extreme  case  being  epigynous 
flowers,  which  are  characteristic  of  the  highest  members  of 
both  Dicotyledons  and  Monocotyledons. 

Many  of  the  variations  of  the  flower  are  associated  with 
the  visits  of  insects  which  feed  upon  the  nectar  or  pollen  of 
flowers  and  thus  become  the  agents  of  cross-pollination. 
This  relation  between  flowers  and  insects  is  often  general, 
but  it  may  be  so  special  that  only  a  particular  kind  of  insect 
can  act  as  the  agent  of  pollination  for  a  particular  kind  of 
flower  (as  among  the  orchids). 

The  use  of  artificial  cross-pollination  in  plant-breeding  is 
to  secure  hybrids  that  combine  certain  desirable  qualities 
of  two  different  kinds  of  parents,  but  the  desired  combination 
usually  appears  in  an  extremely  small  number  of  the  hybrids 
produced. 


CHAPTER  X 
DISPERSAL  AND  GERMINATION  OF  SEEDS 

102.  The  seed  structures.  —  There  are  three  structures 
to  be  considered  in  connection  with  the  seed  (Fig.  117) : 
(1)  the  testa  (seed-coat),  which  is  a  hard  and  resistant  pro- 
tective structure;  (2)  the  endosperm,  which  is  the  tissue 
usually  containing  stored  food ;  and  (3)  the  embryo,  which  is 


FIG.  132.  —  Section  of  bean  with  one  cotyledon  removed,  showing  the  testa  (the  dark 
boundary),  the  remaining  cotyledon  (filling  the  seed  to  the  testa),  the  hypocotyl 
(its  tip  directed  upward),  and  the  plumule  (directed  downward). 

the  young  plant  that  is  to  be  protected  and  fed,  and  which  is 
to  emerge  from  the  seed  and  form  a  new  and  independent 
plant.  The  testa  and  the  embryo  are  always  evident,  but 
sometimes  the  endosperm  has  disappeared.  For  example, 
in  the  cereals  (wheat,  corn,  rice,  etc.)  all  three  structures  are 
present,  and  the  endosperm  contains  the  starch  we  use  for 
food ;  but  in  peas  and  beans  the  endosperm  has  disappeared, 

167 


168  ELEMENTARY   STUDIES   IN   BOTANY 

having  been  consumed  by  the  embryo,  which  occupies  all  the- 
space  of  the  seed  within  the  testa  (Fig.  132).     The  food  we 
obtain  from  peas  and  beans,  therefore,  has  been  transferred 
from  the  endosperm  to  the  embryo  (chiefly  to  the  cotyledons, 
which  form  the  bulk  of  the  embryo). 

The  embryo  is  in  a  dormant  stage ;  that  is,  its  protoplasts 
are  inactive.  With  the  embryos  in  this  condition,  the 
seeds  are  scattered,  and  may  remain  for  a  long  time  without 
showing  any  of  the  ordinary  signs  of  life.  If  stored  in  a  dry 


FIG.  133.  —  Seed-vessel  (fruit) 
of  violet  splitting  into  three 
"valves"  and  discharging  FIG.  134.  —  Pods  of  a  wild  bean  twisting  in 

its  seeds.  —  After  BAILLON.  discharging  seeds.  —  After  BAILLON. 

place,  the  period  of  dormancy  may  be  very  much  prolonged, 
but  in  ordinary  cultivated  plants,  the  best  results  are  ob- 
tained from  seeds  "  planted  "  in  the  year  following  their 
formation.  The  danger  in  keeping  seeds  too  long  is  that  the 
embryos  may  deteriorate,  and  although  the  seeds  look  sound, 
the  young  plants  may  not  be  able  to  grow.  It  is  for  this 
reason  that  "  seed-testing  "  has  become  a  very  important 
business,  to  learn  whether  seeds  offered  for  sale  are  capable 
of  "  germination." 

It  is  evident  that  seed-dispersal  and  seed-germination  are 
the  two  important  topics  in  connection  with  seeds  in  nature. 


DISPERSAL   AND    GERMINATION   OF   SEEDS     169 


In  cultivation,  man  cares  for  the  "  dispersal  "  when  he  plants 
seeds,  but  the  germination  must  be  left  to  nature. 

103.    Seed-dispersal.  —  It  is  a  well.-known  fact  that  seeds 
usually  are  "  scattered,"  which  means  that  they  are  carried 
away  from  the  parent  plant.     The  advantage  of  seed-dis- 
persal, as  the   scattering 
in  nature  is  called,  is  so 

X*??'  obvious  that  it  needs  no 

explanation.     It   is  com- 
, ";l -\  monly  said  that  the  dis- 

persal of  seeds  results  in 
carrying   them   "  beyond 


FIG.    135.  —  Fruit    (akene)    of    a    dandelion 
with  tufts  of  hair.  —  After  KEENER. 


FIG.    136.  —  Fruit    of    Senecio   with 
tufts  of  hair.  —  After  KEENER. 


the  reach  of  rivalry"  with  the  parent  plant.  This  is  certainly 
true,  but  it  probably  carries  them  within  the  reach  of  rivalry 
with  other  plants.  The  safest  thing  to  say  is  that  seed-dispersal 
increases  the  chances  for  successful  seed-germination.  Seed- 
dispersal  involves  not  only  seeds,  but  very  often  fruits  also. 
In  those  fruits  that  open  to  discharge  their  seeds,  the  seeds 
alone  are  carried ;  but  when  fruits  do  not  open,  the  fruit 
itself  is  transported.  The  distances  to  which  seeds  or  fruits 
are  carried  from  the  parent  plants  are  exceedingly  variable, 


170 


ELEMENTARY    STUDIES   IN   BOTANY 


ranging,  from  a  very  short  distance  to  a  very  great  distance, 
as  the  following  illustrations  will  show. 


FIG.  137.  —  Seed  of 
milkweed  with  tuft 
of  hair.  —  After 
GRAY. 


FIG.  138.  —  Seed  ox  nreweed  with  tuft  of  hair. 


In  some  plants  there  is  a  mechanical  discharge  of  seeds 
provided  for  in  the  structure  of  the  seed-vessel  ("  fruit  "). 

For  example,  in  the 
violet,  when  the 
seed-vessel  splits, 
its  walls  press  upon 
the  seeds  so  that 
they  are  pinched 
out,  as  a  moist 
apple-seed  is  pro- 
jected by  being 
pressed  between  the 

FIG.  139.  -  Winged  fruit  of  maple.  -  After  KEENER.         thumb     and     finger 

(Fig.  133).     When  the  pod  of  the  wild   bean  bursts,  the 
two  "  valves  "  twist  violently  and  throw  the  seeds  (Fig.  134). 


DISPERSAL   AND    GERMINATION   OF   SEEDS     171 

In  the  touch-me-not  ("  wild  balsam ")  a  strain  is  devel- 
oped in  the  growing  wall  of  the  seed-vessel,  so  that  at 
rupture,  which  may  be  brought  about  by  a  slight  pressure, 
the  pieces  suddenly  curl  up  and  throw  the  seeds.  This 
mechanical  method  may  be  regarded  as  the  poorest  of  all 
the  methods  of  dispersal,  for  at  the  very  best  a  seed-vessel 
can  discharge  its  seeds  only  a  very  short  distance. 

A  more  effective  method  of  dispersal  and  a  much  more 
common  one  is  by  means  of  currents  of  air.  This  means  that 
seeds  or  fruits  must  be  very  light,  or  that  they  must  develop 


FIG.  140.  —  Winged  seed  of  Bignonia  (a  relative  of  catalpa).  —  After  STRASBURQEK. 

special  appendages  to  aid  in  their  flight.  Among  the  most 
common  appendages  are  tufts  of  hair  and  what  are  very 
naturally  called  "  wings."  For  example,  plumes  and  tufts 
of  hair  are  developed  by  the  seed-like  fruits  of  thistle  and 
dandelion  (Figs.  135  and  136),  and  by  the  seeds  of  milkweeds 
(Fig.  137)  and  fire  weeds  (Fig.  138) ;  while  wings  are  developed 
by  the  fruits  of  maples  (Fig.  139)  and  elms,  and  by  the  seeds 
of  catalpa  (Fig.  140).  An  interesting  modification  of  the 
wind-dispersing  habit  is  exhibited  by  the  "tumble weeds"  or 
" field  rollers"  of  the  western  plains  and  other  level  stretches 
(Fig.  141).  These  plants  are  profusely  branching  annuals 
with  a  small  root  system  in  light  or  sandy  soil.  When  the 
work  of  the  season  is  over,  and  the  rootlets  have  shrivelled, 


172  ELEMENTARY   STUDIES   IN   BOTANY 

the  plant  is  easily  broken  from  its  roots  by  a  gust  of  wind, 
and  is  trundled  along  the  surface  like  a  light  wicker  ball 
(Fig.  141),  the  ripe  seed-vessels  dropping  their  seeds  by  the 
way.  Wind-dispersal  is  far  more  effective  than  mechanical 
discharge,  but  it  is  fitful,  and  its  range  usually  is  not  very 
great.  "  Thistledown  "  may  be  floated  into  a  neighboring 
field,  and  a  strong  wind  may  carry  the  comparatively  heavy- 
winged  fruits  of  the  maple  and  elm  some  distance,  but  at 
best  the  scattering  is  only  over  a  neighborhood. 


FIG.   141.  —  A  common  tumbleweed. 

A  wide-ranging  method  of  dispersal  is  by  means  of  currents 
of  water.  For  example,  the  banks  and  flood-plains  of  streams 
may  receive  seeds  from  a  wide  area,  dependent  upon  the 
extent  of  the  drainage  system.  Along  the  lower  stretches 
of  such  rivers  as  the  Mississippi,  the  Missouri,  and  the  Ohio, 
almost  every  season  new  plants  are  added  to  those  growing 
along  the  banks,  and  some  of  them  may  have  come  from  great 
distances.  This  kind  of  distribution,  therefore,  may  become 
almost  continental  in  extent.  Still  more  far-reaching  is  the 


DISPERSAL  AND   GERMINATION   OF   SEEDS     173 


dispersal  brought  about  by  oceanic  currents,  both  by  waves 
carrying  seeds  along  the  coast,  and  also  by  the  deeper  cur- 
rents that  extend  from  continent  to  continent  or  to  oceanic 
islands.  It  has  been  found  that  many  seeds  can  endure  even 
prolonged  soaking  in  sea-water  and  then  germinate.  From 
a  series  of  experiments,  Darwin  estimated  that  the  seeds  of  at 
least  fourteen  per  cent  of  the  British  plants  can  retain  their 
vitality  in  sea-water  for  twenty-eight 
days.  At  the  ordinary 
rate  of  oceanic  currents, 
this  period  would  per- 
mit seeds  to  be  trans- 
ported over  a  thousand 
miles. 

The  dispersal  of  seeds 
by  means  of  animals  is 
a  very  common  method, 
but  it  is  accomplished 
in  so  many  ways  that 
only  a  very  few  illus- 
trations can  be  given. 
Water  birds  are  great 
carriers  of  seeds,  which 
are  contained  in  the 
mud  clinging  to  their 
feet  and  legs.  This  mud  from  the  borders  of  ponds  is 
usually  filled  with  seeds  of  various  plants.  Water  birds 
are  generally  high  and  strong  fliers,  and  the  seeds  may 
be  transported  in  this  way  to  the  margins  of  distant  ponds 
and  lakes,  and  so  become  very  widely  dispersed.  In  many 
cases,  seeds  or  fruits  develop  grappling  appendages  of  various 
kinds,  forming  the  various  "  burs  "  that  lay  hold  of  animals 
brushing  past,  and  so  the  seeds  become  dispersed.  Common 
illustrations  of  fruits  with  grappling  appendages  are  Spanish 
needles  (Fig.  142),  beggar-ticks  (Fig.  143),  stickseeds,  etc.; 


FIG.  142.  —  Fruit 
(akene)  of  Spanish 
needles  with  barbed 
appendages.  — 
After  KEENER. 


FIG.  143.  —  Fruit  of  beg- 
gar-ticks with  barbed 
appendages.  —  After 
BEAL. 


174  ELEMENTARY   STUDIES   IN   BOTANY 

and  similar  appendages  are  developed  in  connection  with  the 
bracts  about  the  head  of  fruits  of  cocklebur  and  burdock  (Fig. 
144).  Fleshy  fruits  are  attractive  as  food  to  certain  birds 
and  mammals.  Many  of  the  seeds  (such  as  those  of  grapes) 
are  able  to  resist  the  attacks  of  the  digestive  fluids  and  es- 
cape from  the  alimentary  tract  in  a  condition  to  germinate. 
104.  Conditions  for  germination.  —  How  long  seeds  may 
retain  their  vitality  is  a  question  that  cannot  be  answered 
definitely,  for  it  depends  upon  the  kind  of  plant  and  also 
upon  the  conditions  in  which  the  seeds  are  kept.  The  stories 

of  the  germination  of 
wheat  obtained  from  the 
wrappings  of  Egyptian 
mummies  have  proved  to 
be  myths,  but  they  are 
still  in  circulation.  It 
was  a  common  observa- 
tion  that  when  the  origi- 

FIG.  144.  -Heads  of  fruit  of  cocklebur  (A)  and  nal  S°d  °f  the 
burdock  (£),  showing  grappling  appendages  wag  broken  UD  in 
of  the  bracts  (involucre).  —  After  KERNEK. 

ing,  plants  often  sprang 

up  that  seemed  new  to  the  region.  Of  course  such  plants 
came  from  seeds,  and  it  is  possible  that  they  had  been 
kept  for  a  time  in  conditions  unfavorable  for  germination 
until  ploughing  made  the  conditions  favorable.  But 
it  must  be  remembered  that  seeds  are  scattered  over 
wide  areas  every  year,  and  that  "  new  plants  "  may  spring 
up  on  freshly  ploughed  ground  whose  seeds  have  never 
"  waited  "  at  all. 

Three  conspicuous  conditions  for  seed-germination  are 
recognized ;  namely,  moisture,  a  suitable  temperature,  and 
oxygen.  When  seeds  are  "  planted,"  the  soil  is  used  as  the 
most  convenient  source  of  continuous  moisture ;  but  of 
course  seeds  will  germinate  just  as  well  on  moist  blotting 
paper  or  on  moist  sand.  The  soil  has  the  great  incidental 


DISPERSAL  AND   GERMINATION    OF   SEEDS     175 

advantage  in  being  available  for  other  purposes  after  the 
seed  has  germinated  and  the  young  plant  (seedling)  has 
begun  to  manufacture  its  own  food.  The  "  suitable  tem- 
perature "  explains  why  seeds  are  not  planted  out  of  doors 
until  the  "  ground  has  warmed  up  "  a  little.  It  is  well  known 
that  plants  vary  widely  in  the  amount  of  heat  that  is  "  suit- 
able "  for  the  germination  of  their  seeds.  For  example,  some 
seeds  germinate  in  early  spring  or  even  on  the  melting  snow- 
fields  of  alpine  and  arctic  regions,  while  others  need  tropical 
heat.  The  supply  of  oxygen  necessary  comes  in  the  air,  so 
that  there  must  be  free  access  of  air.  This  explains  why  it 
is  necessary  to  have  the  soil  loose,  so  that  there  may  be  a 
free  "  circulation  of  air  "  through  it.  If  the  soil  is  flooded 
with  water,  so  that  there  are  no  free  passageways  for  air, 
seed-germination  is  interfered  with  in  the  same  way  that  an 
air-breathing  animal  is  interfered  with  if  put  under  water. 
If  these  three  conditions  are  supplied,  and  the  seed  is  really 
a  good  one,  it  will  germinate. 

105.  The  entrance  of  water.  —  When  a  seed  has  been 
placed  in  the  proper  conditions  for  germination,  the  first 
visible  result  is  its  swelling  on  account  of  the  entrance  of 
water.     It  must  be  remembered  that  the  protoplasts  of  the 
embryo  and  of  the  endosperm  (if  present)  are  in  a  dormant 
stage,  and  this  stage  is  associated  with  a  lack  of  water,  so 
that  the  protoplasts  are  inactive  (see  §  10,  p.  11).  The  entrance 
of  water  into  the  seed  changes  this  dormant  condition  into  an 
active  condition.     Figuratively  speaking,  the  embryo,  which 
has  been  "  asleep,"  at  least  through  one  winter,  "  wakes  up  " 
and  resumes  its  activity. 

106.  Respiration.  —  The   superficial   indication  that  the 
embryo  has  become  active  again  is  that  oxygen  enters  the 
seed  and  carbon  dioxide  escapes  from  it,  a  gas  exchange  that 
indicates  that  respiration  is  going  on  (see  §  31,  p.  38).     In 
other  words,  the  embryo  shows  that  it  is  alive  and  in  an  active 
condition  by  "  breathing,"  which  is  a  test  of  life  that  we  apply 


176  ELEMENTARY   STUDIES   IN   BOTANY 

to  animals  as  well  as  to  plants.  Not  only  does  the  germinat- 
ing seed  give  off  carbon  dioxide,  but  also  heat.  This  becomes 
very  evident  in  the  process  of  malting,  in  which  a  large  mass 
of  barley  is  put  in  germinating  conditions  in  a  confined  space, 
and  the  total  heat  developed  by  the  mass  of  germinating 
seeds  is  so  great  that  the  water  may  become  scalding  hot. 

107.  Digestion.  —  Before  the  embryo  can  grow,  the  food 
stored  in  the  endosperm  or  in  the  embryo  itself  must  be 
changed  from  its  storage  form  to  its  transfer  form ;  that  is, 
from  an  insoluble  form  to  a  soluble  form,  so  that  it  may  move 
freely  in  solution.     The  process  resulting  in  this  change  is 
called  digestion  (see  §  30,  p.  38).     A  very  common  storage 
form  of  food  in  seeds  is  starch,  and  by  digestion  the  insoluble 
starch  is  converted  into  a  soluble  sugar.     The  active  agents 
in  this  process  are  enzymes,  substances  produced  by  the  pro- 
toplasts, and  the  particular  enzyme  that  converts  the  starch 
of  a  seed  into  sugar  is  diastase.     As  a  result  of  digestion,  the 
seed,  which  had  become  swollen  by  the  entrance  of  water,  is 
observed   to  "  soften."     It  is  at  this  stage  that  the   germi- 
nation of  the  seed  is  checked  in  the  process  of  malting,  which 
thus  secures  the  carbohydrates  of  the  seed  in  the  form  of  a 
solution  of  sugar. 

108.  Assimilation.  —  After  digestion,  the  food  in  solution 
moves  toward  the  active  cells  (protoplasts)  of  the  embryo, 
in  proportion  to  their  activity.     Growth  is  not  uniform  in 
amount  throughout  the  embryo,  so  that  some  regions  receive 
more  food  supply  than  others.     The  most  actively  growing 
region  of  the  embryo  at  first  is  the  hypocotyl  (see  §  75,  p.  126), 
and  in  its  cells  the  protoplasts  are  most  active.     The  pro- 
toplasts  use  the  food  received  by  transforming  it,  step  by 
step,  into  living  protoplasm,  and  it  is  this  process  that  is 
called  assimilation  (see  §  30,  p.  38) .     The  protoplasmic  body 
of  the  protoplast  is  used  up  in  providing  the  materials  for 
growth,  and  therefore  it  must  be  built  up  continually  by 
assimilation. 


DISPERSAL   AND   GERMINATION   OF   SEEDS     177 

109.  Food-storage. -- Thus  far,  only  the  carbohydrate 
starch  has  been  mentioned  as  a  food-storage  form  in  seeds, 
and  it  is  the  most  common  form  in  the  seeds  used  for  food  by 
men.  But  another  conspicuous  group  of  foods  are  the  proteins 
(see  §  29,  p.  37),  and  carbohydrates  are  used  in  the  manufact- 
ure of  proteins  before  protoplasm  can  be  reached.  In  some 
seeds  proteins  are  stored  in  the  form  of  little  grains  (aleurone 
grains).  For  example,  in  a  "  grain  "  of  wheat  (or  of  any 
ordinary  cereal),  the  outer  layer  of  endosperm  cells  contains 
aleurone  grains,  and  the  other  endosperm  cells  contain  starch 
grains.  In  some  seeds,  food  is  stored  in  the  form  of  fats 
in  liquid  form  (oils).  Fats  contain  the  same  chemical  ele- 
ments (carbon,  hydrogen,  and  oxygen)  as  do  the  carbohy- 
drates, but  not  in  the  same  proportion.  Well-known  oils 
obtained  from  seeds  are  castor-oil,  linseed  oil  (from  flax), 
cottonseed  oil,  and  olive  oil. 


FIG.  145.  —  Germinating  beana,  showing  the  hypocotyl ;  the  bean  to  the  left  has  not 
been  moved ;  the  one  to  the  right  was  turned  90°  after  it  had  reached  the  stage  of 
the  other,  and  has  developed  a  curve  in  response  to  the  stimulus  of  gravity. 

110.  Escape  of  the  hypocotyl. — All  of  the  processes 
described  above  as  connected  with  germination  are  prelimi- 
nary to  the  emergence  of  any  part  of  the  embryo  from  the  seed. 
It  was  stated  that  growth  is  most  active  at  first  in  the  hypo- 
cotyl, whose  tip  is  always  directed  towards  that  point  in  the 
seed-coat  where  the  micropyle  of  the  ovule  was  situated,  and 


178 


ELEMENTARY   STUDIES   IN   BOTANY 


which  is  still  called  micropyle  in  the  seed.  It  is  no  longer 
an  open  "  little  gate/'  for  it  has  been  closed  up  during  the 
formation  of  the  testa,  but  it  remains  the  easiest  point  of 
exit  through  the  testa.  Growth  consists  of  cell-division 
followed  by  cell-enlargement.  If  the  cells  of  the  hypocotyl 
all  divide  and  then  each  new  cell  enlarges  to  the  size  of  the 
parent  cell,  the  result  would  be  a  hypocotyl  twice  as  long  and 
twice  as  thick.  Growth,  however,  does  not  proceed  so  uni- 


t 

FIG.  146.  —  A  germination  series  of  the  garden  bean,  showing  roots  developing  from 
the  tip  of  the  hypocotyl,  the  hypocotyl  arch  (pulling  out  cotyledons  and  plumule), 
and  the  straightening  of  the  hypocotyl. 


formly  as  this  throughout  a  whole  structure,  and  the  most 
obvious  result  of  this  early  growth  of  the  hypocotyl  is  its 
rapid  elongation.  This  elongation  speedily  brings  the  tip  of 
the  hypocotyl  against  the  micropyle,  and  then  through  it, 
so  that  the  first  sign  of  the  embryo  outside  of  the  seed  is  the 
emerging  tip  of  the  hypocotyl. 

As  the  hypocotyl  continues  to  elongate,  it  will  be  observed 
to  curve  towards  the  earth,  unless  it  emerged  from  the  seed 
in  that  direction  (Fig.  145).  This  curvature  is  a  response 
by  the  hypocotyl  to  surrounding  influences  (stimuli),  and 


DISPERSAL   AND   GERMINATION   OF   SEEDS     179 


sensitiveness  to  stimuli  is  called  irritability.  The  hypocotyl 
is  a  very  irritable  structure,  and  conspicuous  among  the 
stimuli  to  which  it  responds  are  gravity  and  moisture. 

111.  Geotropism.  —  This  word  means  "  earth-turning," 
and  it  implies  that  there  is  a  turning  (curving)  in  response 
to  the  influence  of  gravity. 
It  should  be  understood  that 
geotropism  is  not  the  "  influence 
of  gravity,"  as  is  sometimes 
stated,  but  it  is  the  response 
of  the  plant  to  the  stimulus  cf 
gravity.  If  the  hypocotyl, 
when  it  emerges  from  the  seed, 
is  directed  upwards  or  horizon- 
tally, gravity  acts  as  a  stimulus 
and  the  irritable  hypocotyl  re- 
sponds by  developing  a  curva- 
ture that  directs  it  downwards. 
The  stimulus  of  gravity,  there- 
fore, results  in  directing  the 
tip  of  the  hypocotyl  towards 
the  soil  and  in  keeping  it  in 
that  direction  (Fig.  145). 

This  is  only  one  way  of  re- 
sponding to  the  stimulus  of 
gravity,  for  a  stem  usually  re- 
sponds by  curving  away  from 
the  earth  and  by  maintain- 
ing this  direction.  These  two 
kinds  of  response  are  distinguished  by  speaking  of  the  hypo- 
cotyl as  positively  geotropic  (its  direction  being  towards  the 
source  of  the  stimulus),  and  of  the  stem  as  negatively  geotropic 
(its  direction  being  directly  away  from  the -source  of  the 
stimulus).  Even  these  two  directions  do  not  include  all  of 
the  responses  to  gravity,  for  branches  of  roots  and  of  stems 


FIG.  147.  —  Germination  of  scarlet-run- 
ner bean  :  first  stage  of  series  shown 
in  Fig.  148 ;  one  cotyledon  removed 
to  show  the  arch  developed  by  the 
first  joint  of  the  stem,  the  stem-tip 
and  leaves  thus  being  freed,  and  the 
cotyledons  remaining  within  the 
testa. 


180 


ELEMENTARY   STUDIES   IN   BOTANY 


are  very  commonly  directed  horizontally,  so  that  they  are 
neither  positively  nor  negatively  geotropic. 

112.  Hydrotropism.  —  This  word  means  "  water-turning," 
and  it  implies  that  there  may  be  a  curvature  in  response  to 
the  influence  of  moisture.  The  hypocotyl  is  sensitive  to 
moisture  and  is  positively  hydrotropic.  Since  ordinarily  the 
stimuli  of  moisture  and  gravity  act  upon  the  hypocotyl 


FIG.  148.  —  Germination  of  scarlet-runner  bean,  the  series  following  the  stage  shown  in 
Fig.  147;  the  elongating  first  joint  of  the  stem  frees  the  stem-tip  and  leaves  and 
finally  straightens ;  the  cotyledons  remain  within  the  seed  coat. 

from  the  same  general  direction,  they  cooperate  in  the 
result,  but  experiments  can  be  devised  to  make  them 
contradictory. 

113.  Development  of  roots.  — When  the  hypocotyl  pene- 
trates the  soil  under  the  joint  directive  influence  of  gravity 
and  water,  the  root  system  begins  to  develop  from  its  tip 
(Fig.  146).  In  some  cases  the  root  continues  the  direction 
of  the  hypocotyl,  being  positively  geotropic,  resulting  in  what 
is  called  a  tap-root;  in  other  cases  it  branches  at  once  in  every 
direction,  and  is  not  at  all  positively  geotropic  in  its  responses. 
In  any  event,  so  far  as  seed-germination  goes,  the  root  an- 


DISPERSAL   AND    GERMINATION   OF   SEEDS     181 

chors  the  seedling  and  establishes  a  grip  on  the  soil  that  is 
necessary  for  the  next  events. 

114.  Escape  of  cotyledons  and  plumule.  —  After  the  root 
with  its  branches  has  anchored  the  seedling  in  the  soil,  the 
hypocotyl  continues  to  elongate  rapidly.  Since  it  is  anchored 


FTG.  149.  —  Seedling  of  castor-bean,  showing  the  large  and  green  cotyledons. 

now  at  both  ends,  one  end  in  the  seed  and  the  other  in  tha 
soil,  elongation  expresses  itself  in  the  development  of  an  arch, 
the  hypocotyl  arch,  which  may  be  observed  very  easily  in  ger- 
minating beans  (Fig.  146).  The  bent  hypocotyl  is  in  a  state 
of  tension,  like  a  bent  spring,  ready  to  straighten  as  soon  as 
it  becomes  free.  This  develops  a  pull  on  the  cotyledons  and 
plumule  within  the  seed,  and  upon  the  roots  in  the  soiL  The 
13 


182 


ELEMENTARY   STUDIES   IN   BOTANY 


root  anchorage  holds  and  the  cotyledons  are  pulled  out  of 
the  seed-coat,  and  when  they  are  free  from  it  the  hypocotyl 
straightens.  The  significant  fact  in  this  escape  is  not  that 
the  cotyledons  are  pulled  out,  for  in  many  seeds  they  remain 
within  the  seed-coat,  but  that  the  plumule  is  pulled  out,  for 

it  develops  the  stem 
and  leaves. 

This  is  only  one 
method  by  which 
the  plumule  be- 
comes free,  but  it 
is  a  common  way, 
and  will  suggest  the 
interpretation  of 
other  methods  that 
ought  to  be  ob- 
served. For  ex- 
ample, in  the  scar- 
let-runner bean  the 
cotyledons  are  not 
usually  freed  from 
the  testa,  the  first 
joint  of  the  stem 
(in  the  plumule) 
developing  the  arch 
and  freeing  the 
stem-tip  and  leaves, 

FIG.  1 50.  —  Germination  of  corn,  showing  superficial 

position  of  embryo,  the  unfolding  leaves,  and  the  aS    may    DC    S66n    in 

roots;    the   single   cotyledon   is  not  seen,    remain-  .        eprip«  cihnwn    in 

ing  in  close  contact  with  the  endosperm.  trie   SCriCS  SnOWn  in 

Figs.  147   and  148. 

Such  seeds  as  those  of  peas,  castor-bean,  squash,  and 
corn  should  be  germinated  to  show  important  variations. 
In  the  pea  and  acorn,  for  example,  the  cotyledons  are  gorged 
with  food  and  are  never  freed  from  the  testa,  but  the  plumule 
is  liberated  by  the  elongation  of  the  bases  of  the  cotyledons 


DISPERSAL  AND   GERMINATION   OF   SEEDS     183 

into  stalks  of  varying  lengths.  In  the  castor-bean  (Fig.  149) 
and  squash,  the  cotyledons  not  only  escape,  but  become  green 
and  work  like  ordinary  leaves.  In  corn,  as  in  all  cereals,  the 
embryo  lies  close  against  one  side  of  the  seed,  so  that  it  be- 
comes completely  exposed  by  the  splitting  of  the  thin  skin 
that  covers  it  (Fig.  150).  In  this  case  the  single  cotyledon  is 
never  freely  expanded,  but  remains  as  an  absorbing  organ 
in  contact  with  the  starch-containing  endosperm. 

With  the  establishment  of  roots  in  the  soil  and  the  exposure 
of  green  leaves  to  light  and  air,  germination  is  over,  for  the 
young  plant  is  now  able  to  make  its  own  food. 

115.  Phototropism.  —  The  stem  of  the  seedling  is  sensitive 
to  the  direction  of  rays  of  light,  and  therefore  it  is  said  to  be 


FIG.  151.  —  A  bean  seedling  that  was  placed  in  a  horizontal  position  and  after  two 
hours  photographed. 


phototropic  ("  light-turning  ").  It  is  not  light  in  general 
that  acts  as  a  stimulus,  but  the  direction  of  the  rays  of  light. 
The  response  of  the  stem  to  this  stimulus  is  to  curve  directly 
towards  the  source  of  the  light  rays,  and  therefore  it  is  posi- 
tively phototropic.  Figure  151  shows  a  bean  seedling  placed 
in  a  horizontal  position  and  after  two  hours  photographed ; 
while  Figure  152  shows  the  same  seedling  completely  inverted 
and  photographed  after  two  days. 

The  root  is  also  -photo tropic,  turning  directly  away  from 
the  source  of  light;  that  is,  it  is  negatively  phototropic. 
Figure  153  shows  a  seedling  of  a  white  mustard  so  arranged 
that  both  stem  and  root  are  exposed  only  to  weak  light,  the 


184 


ELEMENTARY   STUDIES   IN   BOTANY 


former  showing  positive  and  the  latter  negative  phototropism, 

as  explained  more  fully  in  the  legend. 

By  putting  together  the  results  of  the  various  tropisms, 

it  is  evident  that  an  irritable  structure  (as  a  growing  stem 

or  root)  responds  to  several  of  them  at  the  same  time.     The 

tap-root,  for  example,  has  been 
shown  to  respond  to  the  stimulus 
of  gravity,  of  moisture,  and  of  light, 
and  each  response  directs  it  into 
the  soil,  so  that  its  direction  is  de- 
termined by  the  sum  of  all  these 
stimuli.  In  the  same  way,  the  stem 
is  not  only  positively  phototropic, 
but  also  negatively  geotropic,  so 


FIG.  152. —  The  same  seedling 
shown  in  Fig.  151,  completely 
inverted,  and  after  two  days 
photographed. 


FIG.  153.  —  Seedling  of  white  mustard  grown  in 
water  and  exposed  to  weak  light,  showing  that 
the  stem  is  positively  phototropic  and  the  root 
negatively  phototropic  ;  the  arrows  indicate  the 
direction  of  the  rays  of  light. 


that   the   sum   of    these   stimuli   determines   the   direction 
away  from  the  soil. 

It  was  stated  that  all  roots  are  not  positively  geotropic, 
for  root  branches  frequently  grow  horizontally.     In  the  same 


DISPERSAL  AND   GERMINATION  OF  SEEDS     185 

way,  all  structures  of  the  stem  are  not  positively  phototropic, 
for  many  branches  grow  horizontally,  and  leaf  blades  are  very 
commonly  horizontal.  When  it  is  remembered,  however, 
that  groups  of  stimuli  act  on  organs,  and  that  not  all  of  them 
may  be  influencing  the  organ  in  the  same  direction,  it  will 
be  understood  that  the  actual  direction  is  a  resultant  and 
not  necessarily  the  direction  that  would  be  determined  by 
any  stimulus  acting  alone. 

It  should  be  kept  in  mind  that  stimuli  which  influence  direc- 
tion call  forth  an  evident  response  only  when  the  organ  is  out 
of  line,  and  the  response  (reaction)  is  a  curve  that  brings  it 
back  into  line.  The  sensitive  or  irritable  region  of  an  organ 
is  not  necessarily  the  region  where  the  reaction  occurs ; 
for  example,  the  root  tip  is  the  sensitive  region  that  "  per- 
ceives "  the  stimulus,  but  the  reaction  appears  in  a  curve 
at  some  distance  from  the  tip.  Nor  does  the  reaction  follow 
the  stimulation  immediately,  for  there  is  an  interval,  known 
as  reaction  time,  which  is  generally  much  longer  in  plants 
than  in  animals.  The  reaction  may  be  several  hours,  but 
in  some  cases  it  may  be  very  short,  as  the  movement  of  the 
leaves  of  the  sensitive  plant  (§  125,  p.  213),  and  the  snap- 
ping shut  of  the  leaves  of  Dioncea  (§  127,  p.  222). 

116.  The  hypocotyl.  —  Any  study  of  the  germination  of 
the  seed  impresses  the  fact  that  the  hypocotyl  is  the  most 
important  organ.     It  is  distinctly  an  organ  of  the  embryo, 
for  its  work  is  over  when  germination  has  been  completed. 
Its  importance  lies  in  the  fact  that  it  relates  the  seedling 
effectively  to  its  surroundings,  that  is,  it  "  orients  "  the  seed- 
ling.    It  puts  the  root  in  the  soil  and  it  often  liberates  the 
plumule  so  that  the  stem  may  begin  to  develop  its  succes- 
sion of  leaves  in  relation  to  air  and  light.     When  the  seedling 
has  thus  been  started  in  the  right  directions,  the  hypocotyl 
disappears  as  a  distinct  structure,  and  the  plant  body  con- 
sists of  root,  stem,  and  leaves. 

117.  Summary.  —  The  chances  of  the  successful  germina- 


186  ELEMENTARY    STUDIES   IN   BOTANY 

tion  of  seeds  are  increased  by  dispersing  them,  and  this 
dispersal  is  provided  for  in  various  ways.  Some  seeds  are 
discharged  mechanically ;  many  seeds  (or  fruits)  are  equipped 
with  tufts  of  hair  (plumes)  or  wings  for  air-dispersal ;  many 
seeds  (or  fruits)  are  carried  by  currents  of  water,  and  in 
the  case  of  oceanic  currents  they  may  be  carried  great  dis- 
tances ;  and  many  seeds  (or  fruits)  are  carried  away  from 
the  parent  plant  by  animals.  It  must  be  remembered, 
however,  that  many  seeds  and  fruits  fall  to  the  ground  from 
the  parent  plant  and  are  not  dispersed  at  all. 

The  process  called  seed-germination  extends  from  the 
starting  of  a  dormant  embryo  into  activity  to  the  beginning 
of  food  manufacture  by  the  young  seedling.  The  conditions 
necessary  for  germination  are  moisture,  free  access  of  air 
(oxygen),  and  a  suitable  temperature,  and  for  most  plants 
this  combination  is  best  secured  by  burial  in  loose  soil.  The 
entrance  of  water  enables  the  dormant  protoplasts  to  be- 
come active  again,  and  this  activity  is  evidenced  by  respira- 
tion. The  first  result  of  activity  is  the  digestion  of  stored 
food  which  then  passes  into  the  active  protoplasts  and  be- 
comes assimilated.  As  a  result,  the  growth  of  the  embryo 
begins,  the  tip  of  the  hypocotyl  emerges  from  the  seed,  the 
root  is  established,  the  plumule  (and  often  the  cotyledons) 
are  pulled  out  of  the  seed-coat,  and  when  the  seedling  begins 
to  manufacture  its  own  food,  germination  is  over. 


CHAPTER  XI 
LEAVES 

118.  General  features.  —  It  is  not  necessary  to  define 
what    is    meant    by    foliage    leaves,    for    no    structure    of 
plants  is  more  familiar.     They  are  thought  of  by  botanists 
as  expansions  of  green  tissue  exposed  to  light  and  air,  and 
especially  concerned  in  the  manufacture  of  food.     Every- 
thing important  connected  with  a  foliage  leaf  is  to  be  ex- 
plained by  this  fact,  for  arrangement,  position,  form,  and 
structure  are  all  related  to  the  work  of  food  manufacture. 
A  consideration  of  leaves  has  been  deferred  until  the  Angio- 
sperms  can  be  included,  for  it  is  in  this  great  group  that 
the  largest  display  of  leaves  is  found. 

The  variation  in  the  form  and  structure  of  leaves  is  so 
great  that  they  are  useful  in  classification,  and  for  this  rea- 
son numerous  technical  terms  have  been  devised  to  indicate 
these  variations  with  precision.  However,  to  learn  the  defi- 
nitions of  all  these  terms  is  not  to  know  a  leaf  and  its  work, 
and  therefore  in  this  presentation  they  are  disregarded  except 
so  far  as  some  of  them  may  be  of  service. 

119.  General  structure.  —  It  is  a  matter  of  common  ob- 
servation that  the  green  expansion  called  a  leaf  may  arise 
either  directly  from  the  stem  or  it  may  have  a  stalk  of  its. 
own  (petiole).     The  presence  or  absence  of  a  petiole  (Fig. 
154)  is  related  to  the  exposure  of  the  leaf,  and  has  nothing 
to  do  with  the  structure  of  the  leaf  for  the  work  of  food 
manufacture. 

If  the  leaf  is  examined  superficially,  it  will  be  seen  that 

187 


188 


ELEMENTARY   STUDIES   IN   BOTANY 


through  the  green  tissue  there  extend  "  veins  "  (Fig.  154),  as 
described  in  §  55  (p.  90).     These  veins  are  extensions  of  the 
vascular  system,  and  carry  water  to  the  green  tissue.     It  is 
\  necessary,   therefore,  that  the  veins  branch  sufficiently  to 
\reach  all  the  working  cells.     How  completely  this  is  accom- 
plished may  be  seen  in  a  "  skeletonized  "  leaf,  from  which 


^11  the  green  tissue  has  been  removed,  and  only  the  veins 


C 


FIG.  154.  —  A,  pinnate  leaf  of  quince,  which  is  entire  and  has  a  short  petiole;  B, 
palmate  leaf  of  geranium,  which  is  lobed  and  has  a  long  petiole ;  C,  parallel-veined 
leaf  of  lily-of-the-valley.  —  After  GRAY. 

remain  (Fig.  155).  Incidentally,  but  very  necessarily,  the 
vein  system  forms  a  stiff  framework  to  support  the  expanded 
green  tissue,  which  otherwise  would  collapse.  That  the  veins 
are  not  the  only  mechanical  support  is  evident  when  a  leaf 
wilts,  a  thing  which,  as  every  one  knows,  is  due  to  a  lack  of 
water.  For  an  ordinary  foliage  leaf  to  keep  its  expanded 
form,  the  working  cells  must  be  gorged  with  water,  and  much 
of  the  stiffness  of  a  broad  leaf  is  due  to  this  turgor  (§  10, 
p.  10)  of  the  cells.  The  green  tissue,  therefore,  is  kept  spread 


LEAVES 


189 


out  not  only  by  the  framework  of  the  water-conducting 
vessels,  but  also  by  the  turgor  of  its  cells. 

The  general  shape  of  a  leaf  is  largely  determined  by  the 
character  of  its  vein  system,  and  although  the  kinds  of  vein 
systems  are  numerous,  the  three  most  common  ones  may  be 
noted.  In  one  kind,  a  large  main  vein  runs  through  the  center 
of  the  leaf,  and  smaller  veins  arise  from  it  on  either  side, 
branching  in  turn  (Fig.  154,  A).  For  convenience,  the  large 
main  veins  are  called  ribs,  and 
the  solitary  central  rib  in  the 
case  just  described  is  called  a 
midrib.  Leaves  with  midribs  are 
called  pinnate,  because  the  vein 
system  is  like  a  feather,  with  its 
central  shaft  and  branches,  and 
such  leaves  are  apt  to  be  com- 
paratively narrow  and  elongated. 
In  another  kind  of  vein  system 
several  ribs  of  equal  prominence 
start  out  at  the  base  of  the  leaf 
and  diverge  more  or  less  widely, 
each  giving  rise  to  branches  (Fig. 
154,  B).  Such  leaves  are  called 
palmate,  because  the  ribs  suggest 
the  spread  fingers  arising  from  the 

palm  of  the  hand,  and  they  are  apt  to  be  broad  and  com- 
paratively short.  In  a  third  kind  of  vein  system  there 
are  no  especially  prominent  ribs,  but  the  veins  run  ap- 
proximately parallel  through  the  leaf  from  base  to  apex 
(Fig.  154,  C).  These  "  parallel  "  veins  are  not  the  only 
veins,  but  the  branches  ("  veinlets ")  that  arise  from 
them  are  so  small  that  they  are  not  visible  to  ordinary 
observation.  Such  leaves  are  said  to  be  parallel-veined, 
and  they  are  always  comparatively  narrow  and  elongated, 
as  in  lilies  and  grasses. 


FIG.  155.  —  Portion  of  a  skeletonized 
leaf  (Ficus),  showing  the  network 
of  veins,  and  also  the  free  end- 
ings of  veins  (open  system). 


190 


ELEMENTARY   STUDIES   IN   BOTANY 


The  pinnate  and  palmate  leaves  are  often  called  net- 
veined  leaves,  to  distinguish  them  from  the  parallel-veined 
leaves,  but  really  they  are  all  net-veined  leaves,  the  dif- 
ference being  that  in  pinnate  and  palmate  leaves  the  network 
of  veins  is  visible,  while  in  parallel-veined  leaves  it  is  invisible. 
It  is  a  common  statement  that  Dicotyledons  have  pinnate 
and  palmate  leaves,  while  Monocotyledons  have  parallel- 
veined  leaves.  This 
is  generally  true  of 
Angiosperms  that 
grow  in  temperate  re- 
gions, but  when  tropi- 
cal plants  are  included, 
the  distinction  van- 
ishes, for  the  banana 
has  good  pinnate 
leaves  and  the  palm 
leaf  used  for  "  palm 
leaf  fans"  is  palmate, 
and  both  of  these 
plants  are  Monocoty- 
ledons. The  real  leaf 
distinction  between 
Monocotyledons  and 
Dicotyledons  is  that 
in  Dicotyledons  the  veinlets  end  freely  in  the  margin  of  the 
leaf  (as  well  as  elsewhere),  forming  an  "  open  system  "  of 
veins'  (Fig.  155) ;  while  in  Monocotyledons  the  veinlets  do 
not  end  freely,  but  are  all  part  of  a  "closed  system." 

One  of  the  notable  differences  among  leaves  is  that  the 
margins  of  some  of  them  are  variously  toothed  or  lobed, 
while  in  others  they  are  not.  In  the  latter  case  the  leaf  is- 
said  to  be  entire  (Fig.  154,  A  and  C).  Leaves  with  a  closed 
system  of  veins  are  always  entire,  which  means  that  most  of 
the  Monocotyledons  have  entire  leaves.  Leaves  with  an 


FIG.  156.  —  Compound  (branching)  leaves:  A,  pin- 
nately  compound  leaf  of  black  locust ;  B,  pal- 
mately  compound  leaf  of  red  clover. 


LEAVES 


191 


open  system  of  veins  may  be  entire,  but  often  develop  a 
toothed  margin  in  connection  with  the  free  endings  of  the 
vein  system,  which  means  that  toothed  and  lobed  leaves 
(Fig.  154,  B)  are  characteristic  of  Dicotyledons.  Leaves 
with  an  open  system  of  veins  may  not  only  become  toothed 

or  lobed,  but  the  lobing  may  be  _ 

carried  so  far  that  the  blade  be- 
comes discontinuous  (Fig.  156), 
and  appears  as  if  broken  up  into 
several  blades  (leaflets).  Such 
leaves  are  said  to  be  compound, 
but  they  are  better  called  branch- 
ing leaves.  The  results  of  this 
branching  habit  of  leaves  are 
related  to  the  character  of  the 
vein-system.  In  pinnate  leaves 
with  open  venation,  branching 
may  result  in  elongated  forms 
with  very  numerous  leaflets; 
while  in  palmate  leaves  with  open 
venation,  branching  results  in 
broad  forms  and  a  more  restricted 
number  of  leaflets.  This  differ- 
ence and  the  reason  for  it  be- 
come very  evident  when  the 
pinnately  branching  leaf  of  black 
locust  (Fig.  156,  A)  is  compared  with  the  palmately 
branching  leaf  of  red  clover  (Fig.  156,  B).  Of  course  the 
branches  in  each  case  may  branch  again,  and  thus  the  leaf 
may  become  quite  extensive,  with  very  numerous  leaflets. 
The  most  familiar  illustrations  are  probably  the  extensively 
branching  leaves  of  many  ferns. 

120.  Internal  structure.  —  The  foliage  leaf  is  a  very 
efficient  machine,  and  it  is  necessary  to  understand  the  general 
arrangement  of  its  cells.  To  observe  this  most  easily,  thin 


FIG.  157.  —  Cross-section  of  a  lily 
leaf,  showing  the  epidermis  above 
and  below,  with  three  stomata  in 
the  lower  epidermis ;  between 
the  epidermal  layers  the  meso- 
phyll  (the  cells  containing  chloro- 
plasts),  with  a  layer  of  palisade 
cells  against  the  upper  epidermis, 
and  below  this  the  spongy  tissue 

'  with  air-spaces  of  various  sizes 
(the  stomata  open  into  three 
large  ones) ;  imbedded  in  the 
mesophyll  are  sections  of  two 
veinlets,  the  group  of  xylem  ves- 
sels (water-conducting)  being  at 
the  upper  side  of  each  veinjet. 


192  ELEMENTARY   STUDIES   IN   BOTANY 

sections  through  some  relatively  thick,  spongy  leaf,  like  that 
of  hyacinth  or  of  lily,  should  be  made.  In  such  sections 
even  a  low  power  of  the  microscope  will  show  three  distinct 
regions  (Fig.  157). 

(1)  Epidermis.  —  Bounding  each  side  of  the  leaf  is  a  layer 
of  cells  fitting  closely  together  and  usually  without  chloro- 
plasts  (Fig.  157).  This  is  the  epidermis,  which  is  like  a  layer 
of  water-proof  material  preventing  excessive  loss  of  water 
from  the  working  cells  within.  The  resistance  to  the  escape 
of  water  is  much  increased  by  a  substance  formed  on  the  outer 
walls  of  the  epidermal  cells,  known  as  cutin,  which  forms  a 
covering  of  the  epidermis  called  cuticle.  This  layer  of 


FIG.  158.  —  Section  through  a  small  portion  of  a  yew  leaf,  showing  the  epidermis  (e) 
with  its  thick  cuticle  (c),  and  the  upper  part  of  the  palisade  layer  (p). 


cuticle  makes  the  outer  epidermal  walls  look  thick,  and  the 
thicker  it  is  the  more  resistant  is  the  leaf  to  the  loss  of  water 
(Fig.  158).  In  plants  of  dry  regions  the  cuticle  may  become 
excessively  thick.  An  epidermis  overlaid  by  cuticle  forms 
not  only  a  water-tight  layer,  but  also  an  air-tight  one.  It  is 
evident  that  the  cells  at  work  in  food  manufacture  cannot 
be  shut  off  from  the  air,  for  there  must  be  an  intake  of  carbon 
dioxide  and  an  outgo  of  oxygen.  For  this  reason,  there  is 
developed  in  the  epidermis  a  set  of  guarded  openings,  the 
stomata  (singular  stoma). 

.  The  general  outline  of  a  stoma  may  be  seen  by  peeling 
off  the  epidermis  and  examining  it  in  surface  view  rather 
than  in  section  (Fig.  159).  In  surface  view  it  appears  as 
two  crescentic  epidermal  cells  forming  between  them  a  slit- 


LEAVES 


193 


like  opening.  These  cells  are  called  guard-cells,  because  they 
regulate  the  size  of  the  opening.  When  seen  in  the  cross- 
section  of  the  epidermis,  the  stomata  appear  as  pairs  of  small 
cells  interrupting  the  epidermal  layer  (Fig.  157).  The  guard- 
cells  usually  project  toward  one  another  near  the  centre  of 
their  depth,  so  that  the  opening  between  them  funnels  down 
to  a  narrow  slit  and  then  enlarges,  on  the  general  plan  of 
an  hour-glass.  The  guard-cells  can  change  their  shape, 
and  so  enlarge  or  diminish  the  opening  between  them.  It 


FIG.  159.  —  Surface    view  of  epidermis  of   a  hyacinth    leaf:    A,  elongated   epidermal 
cells  and  four  stomata  with  their  guard-cells ;   B,  enlarged  view  of  a  single  stoma. 

is  the  stomata  that  provide  passageways  into  the  interior 
of  the  leaf,  solving  the  problem  of  the  epidermis  how  to 
prevent  excessive  loss  of  water  and  at  the  same  time  main- 
tain communication  with  the  air. 

The  number  of  stomata  is  a  very  important  feature  of  the 
mechanism  of  a  leaf,  for  it  is  found  that  very  numerous  small 
openings  over  a  given  area  are  as  effective  in  gas  exchanges 
as  if  the  whole  area  were  open.  A  fair  average  number  of 
stomata  is  about  100  to  each  square  millimeter  of  surface 
(about  62,500  to  the  square  inch) ;  and  in  some  cases  the 
number  may  reach  700  to  the  square  millimeter  (almost 
450,000  to  the  square  inch).  When  it  is  remembered  that 


194  ELEMENTARY    STUDIES   IN    BOTANY 

stomata  are  to  permit  communication  with  the  air  without 
permitting  an  excessive  loss  of  water,  their  distribution  be- 
comes a  matter  of  course.  For  example,  in  horizontal 
leaves,  the  stomata  are  chiefly  and  sometimes  exclusively 
on  the  under,  more  shaded,  surface,  a  surface  less  dangerous 
to  open  to  the  drying  air  than  the  upper  surface ;  on  erect 
leaves  (as  iris),  in  which  both  surfaces  are  exposed  alike  to 
the  light,  the  stomata  are  equally  distributed ;  in  floating 
leaves  (as  water-lilies)  the  stomata  are  naturally  all  on  the 
upper  surface ;  while  in  submerged  leaves  there  are  no 
stomata  at  all.  Stomata  are  not  peculiar  to  the  epi- 
dermis of  leaves,  for  they  are  found  in  the  epidermis  of  any 
green  part,  as  young  stems,  fruit,  etc.,  and  even  on  the  petals 
of  flowers. 

(2)  MesophylL  —  Between  the  two  epidermal  layers  is 
the  mass  of  green  tissue  making  up  the  body  of  the  leaf 
(Fig.  157),  and  called  mesophyll  ("  middle  region  of  leaf  "). 
Of  course  it  is  these  cells  that  contain  the  chloroplasts  and 
are  the  working  cells  that  the  epidermis  protects  against 
the  drying  effect  of  air,  and  to  which  the  stomata  permit 
access  of  air.  In  horizontal  leaves,  the  cells  of  the  meso- 
phyll usually  are  arranged  differently  in  the  upper  and  lower 
regions  of  the  leaf.  Those  in  contact  with  the  upper  epider- 
mis are  elongated  at  right  angles  to  the  surface  of  the  leaf 
and  stand  in  close  contact,  being  the  palisade  cells  (Fig.  157). 
The  mesophyll  cells  beneath  the  palisade  layer  are  irreg- 
ular in  form,  and  so  loosely  arranged  as  to  leave  air-spaces 
between  the  cells,  the  whole  region  forming  the  spongy  tissue 
(Fig.  157).  The  air-spaces  communicate  with  one  another, 
forming  a  labyrinth  of  air-passages  throughout  the  spongy 
mesophyll.  It  is  into  this  system  of  air-passages  that  the 
stomata  open  (Fig.  157),  so  that  all  of  the  green  cells  are 
put  in  contact  with  the  air.  The  picture  of  a  l^af^a  food- 
manufacturing  machine,  therefore,  is  that  of/^an  internal 
and  moist  atmosphere  bathing  the  working  cells  and  com- 


LEAVES  195 

municating  with  the  external  atmosphere  through  the  sto- 
mata,  which  are  able  to  regulate  the  freedom  of  this  com- 
munication. Through  this  mechanism,  the  carbon  dioxide 
of  the  external  atmosphere  diffuses  into  the  internal  atmos- 
phere of  the  leaf  and  passes  into  the  working  cells,  while 
the  oxygen  that  passes  from  the  cells  into  the  internal  at- 
mosphere diffuses  into  the  external  atmosphere. 

(3)  Veins.  —  In  the  cross-section  of  the  leaf  there  appear 
sections  of  the  veins  of  various  sizes,  embedded  in  the  meso- 
phyll  at  varying  intervals  (Fig.  157).  It  has  been  stated 
that  the  veins  bring  to  the  mesophyll  cells  water  that  has 
come  from  the  soil.  It  will  be  seen  that  the  water-con- 
ducting part  (xylem)  of  these  vascular  strands  is  towards 
the  upper  surface  of  the  leaf,  the  natural  position  when  it 
is  remembered  that  the  strand  arises  from  the  stem  cylinder, 
where  the  xylem  is  on  the  inside,  and  turns  outward  into 
the  horizontal  leaf. 

121.  Photosynthesis.  —  The  manufacture  of  carbohydrate 
food  by  green  plants  was  outlined  in  Chapter  III  (p.  31)  in 
connection  with  Algae,  so  that  it  need  not  be  repeated  here. 
However,  it  should  be  remembered  that  the  process  de- 
scribed there  is  not  only  carried  on  by  the  leaf,  but  that  the 
leaf  is  a  particularly  efficient  machine  for  photosynthesis 
in  plants  exposed  freely  to  the  air.  Water  is  carried  in  from 
the  soil,  carbon  dioxide  diffuses  from  the  external  atmosphere 
to  the  internal  atmosphere  through  the  stomata,  the  chloro- 
plasts  in  the  mesophyll  cells  lay  hold  of  these  materials  with 
energy  obtained  from  light  and  manufacture  a  carbohydrate, 
the  oxygen  waste  diffuses  from  the  internal  atmosphere  to 
the  external  atmosphere,  and  the  whole  living  machine  is 
kept  from  drying  out  by  the  epidermis  with  its  layer  of 
cuticle. 

122. »  Transpiration.  —  Although  water  is  being  evaporated 
constantly  from  the  surface  of  a  living  plant  exposed  to  the 
air,  foliage  leaves  are  especially  exposed  to  this  evaporation 


196 


ELEMENTARY    STUDIES   IN   BOTANY 


(transpiration),  so  that  the  loss  by  the  leaves  represents  the 
largest  amount  of  loss  in  an  ordinary  plant.  It  has  been 
stated  that  the  epidermis  with  its  cuticle  checks  transpira- 
tion, but  it  does  not  prevent  it  entirely.  The  greatest 
amount  of  transpiration,  however,  is  by  way  of  the  stomata, 

for  the  water  vapor 
of  the  internal  at- 
mosphere, obtained 
from  the  cells,  is 
diffusing  continually 
into  the  external 
atmosphere.  If  the 
stomata  are  closed 
by  the  guard-cells 
and  the  internal  at- 
mosphere becomes 
saturated  with  wrater 
vapor,  the  loss  of 
water  from  the  work- 
ing cells  is  very  little 
or  none  at  all.  It 
is  evident  that  the 
larger  the  air-spaces 
in  the  leaf,  that  is, 
the  looser  the  leaf  is 
in  texture,  the  greater 
is  the  amount  of 
internal  atmosphere, 
and  the  more  rapid 
is  transpiration.  Hence  the  amount  of  transpiration  from 
a  leaf  depends  more  upon  its  structure  than  upon  the  extent 
of  its  exposed  surface. 

A  simple  experiment  should  be  performed  to  demonstrate 
the  fact  of  transpiration  by  placing  a  glass  vessel  (bell  jar) 
over  a  small  active  plant,  care  being  taken  to  shut  off  the 


FIG.  160.  —  Transpiration  experiment :  a  potted  ge- 
ranium sealed  with  a  rubber  cloth  and  covered 
with  a  bell  jar;  the  mist  and  droplets  of  water  on 
the  glass  more  or  less  obscure  the  plant. 


LEAVES 


197 


evaporation  from  the  pot  and  soil  by  a  rubber  cloth  (Fig. 
160)  or  some  other  device.  Moisture  will  be  seen  to  collect 
on  the  glass  and  even  to  trickle  down  the  sides.  Some  meas- 
urements of  the  loss  of  water  by  transpiration  are  as 
follows :  a  single  stalk  of  corn  lost  four  gallons  of  water  in 
173  days  (the  duration  of 
its  life) ;  a  single  hemp 
plant  lost  nearly  eight  gal- 
lons in  140  days ;  a  sun- 
flower, whose  leaf  surface 
was  approximately  nine 
square  yards,  gave  off 
nearly  one  quart  of  water 
in  a  single  day.  If  such 
measurements  be  applied 
in  a  general  way  to  tho 
enormous  area  of  leaf  ex- 
posure in  a  forest,  or  to  any 
great  mass  of  vegetation, 
some  vague  idea  may  be 
obtained  as  to  the  enor- 
mous volume  of  water  vapor 
that  is  being  given  off  by 
plants. 

Transpiration  has  been 
regarded  usually  as  a  men- 
ace to  the  plant,  without 
any  corresponding  advan- 
tage. It  was  known  that 
wate,r  must  be  supplied 

freely  to  the  working  cells  to  keep  them  in  working  condition, 
as  well  as  to  supply  to  green  cells  the  water  used  in  photo- 
synthesis, and  it  was  realized  that  loss  of  water  by  evapo- 
ration is  inevitable.  It  has  been  demonstrated  recently  that 

transpiration  is«not  so  much  a  danger  to  the  plant  that  must 
14 


FIG.  161.  —  A  broad-leaved  plant,  showing 
the  general  horizontal  plane  of  the  leaf- 
blades. 


198 


ELEMENTARY    STUDIES   IN   BOTANY 


be  guarded  against,  as  a  means  by  which  the  working  cells 
are  kept  at  a  working  temperature.  It  is  found  that  the 
heat  from  the  sunlight  would  raise  the  temperature  of  a 
leaf  dangerously  if  it  were  not  tempered  by  the  cooling 
effect  of  transpiration.  Experiments  show  that  if  tran- 
spiration is  stopped,  leaves  perish  quickly.  Transpiration, 
therefore,  is  a  protection  of  very  great  importance ;  while 


FIG.  162.  —  Leaves  of  geranium  shifting  position  according  to  the  direction  of  the 
light :  A,  the  plant  exposed  to  vertical  rays  of  light ;  B,  the  same  plant  exposed  to 
oblique  rays  of  light. 

/• 

the  danger  of  transpiration  is  simply  that  the  supply  of 
water  may  not  be  equal  to  the  necessary  and  beneficial  loss. 
Another  very  important  advantage  of  transpiration  is 
that  the  continual  loss  of  water  from  the  leaves  results  in 
a  continual  movement  of  water  into  the  leaves.  This  mass 
movement  of  water  in  the  plant  towards  the  regions  of  loss 
(the  regions  of  transpiration)  is  often  called  the  transpira- 
tion current.  This  does  not  explain  how  the  water  moves 


LEAVES  199 

so  much  as  the  direction  in  which  it  moves.  The  importance 
of  this  mass  movement  of  water  not  only  consists  in  making 
good  the  loss  through  transpiration  and  thus  insuring  the 
continuation  of  transpiration,  but  also  it  carries  to  the  work- 
ing cells  the  soil  materials  especially  necessary  in  the  manu- 
facture of  proteins. 

123.  Exposure  to  light.  —  It  is  evident  that  leaves  should 
be  so  adjusted  as  to  receive  as  much  light  as  possible  without 
danger,  for  too  intense  light  is  dangerous.  It  is  a  problem 
of  "  just  enough  and  not  too  much."  The  adjustment  to 


FIG.  163.  —  Rosette  of  mullein  (A)  and  of  evening  primrose  (B). 

light,  therefore,  is  a  delicate  one,  for  the  exact  position  any 
particular  leaf  holds  in  relation  to  light  depends  upon  many 
circumstances,  and  cannot  be  covered  by  a  general  rule, 
except  that  it  should  get  all  the  light  it  can  without  danger. 

The  ordinary  plane  of  a  leaf  is  approximately  horizontal 
(Fig.  161),  a  position  which  enables  it  to  receive  the  direct 
and  most  intense  rays  of  light  upon  its  upper  surface.  Cer- 
tainly in  this  position  more  rays  strike  the  leaf  than  if  its 
plane  were  oblique  or  vertical,  the  latter  position  often  being 
spoken  of  as  an  "  edgewise  "  position.  Most  leaves  when 
fully  grown  are  in  a  fixed  position  that  has  been  determined 
by  the  conditions  that  prevailed  during  their  development. 


200 


ELEMENTARY   STUDIES   IN   BOTANY 


But  some  leaves  are  so  constructed  that  they  can  shift  their 
position  as  the  direction  of  the  light  changes,  or  the  stem 
bearing  the  leaves  may  shift  its  position  so  that  a  better 
relation  to  light  is  secured  (Fig.  162).  The  leaves  of  window 
plants  are  often  seen  to  adjust  themselves  so  as  to  face  the 
light,  and  by  turning  such  a  plant  around  so  as  to  bring  its 
other  side  towards  the  light,  the  leaves  will  become  adjusted 
gradually  to  the  new  condition  and  face  the  light  again. 

It  is  evident  that  the  leaves  of  a  plant  are  in  danger  of 
shading  one  another,  and  while  shading  cannot  be  avoided, 

it  can  be  diminished 
in  various  ways.  The 
spacing  apart  of  the 
leaves  by  the  elonga- 
tion of  the  internodes 
(§  130,  p.  224)  is  the 
most  general  method 
of  avoiding  extreme 
shading.  The  spiral 
arrangement  of  leaves 
on  the  stem,  which 
prevents  two  succes- 
sive leaves  from  stand- 
ing in  the  same  plane, 
is  also  a  very  general  method  of  diminishing  shading  (Fig.  161). 
In  many  herbs  whose  leaves  are  rather  large  and  close 
together,  the  petioles  of  the  lower  leaves  are  usually  longer 
than  those  above,  and  thus  their  blades  are  thrust  beyond 
the  shadow  of  the  upper  leaves.  The  same  result  is  obtained 
when  the  lowest  leaves  of  a  plant  are  the  largest,  and  the 
upper  leaves  gradually  diminish  in  size. 

Some  plants  are  in  such  a  position  that  for  protection  (to  be 
explained  later)  the  leaves  are  produced  in  a  cluster  at  the 
base  of  the  stem.  This  is  called  the  rosette-habit,  and  the 
rosette  of  leaves  frequently  lies  flat  upon  the  ground  or  upon 


FIG.  164.  —  Rosette  of  shepherd's  purse. 


201 


202 


ELEMENTARY    STUDIES    IN   BOTANY 


the  rocks  (Figs.  163  and  164).  This  close  overlapping  of 
leaves  is  a  very  poor  adjustment  to  light  at  best,  but  there 
is  evident  an  adjustment  to  secure  the  most  light  possible 
under  the  circumstances.  The  lowest  leaves  of  the  rosette 
are  the  longest,  and  the  upper  ones  become  gradually  shorter, 
so  that  each  leaf  has  at  least  a  part  of  its  surface,  and  usually 
the  broadest  part,  exposed  to  light. 


FIG.  166.  —  The  leaf-mosaic  of 


Fittonia;   observe  also  the  beautifully  distinct 
veining. 


All  of  these  adjustments  to  light  may  be  brought  together 
under  the  conception  of  a  leaf-mosaic,  by  which  is  meant  the 
arrangement  of  leaf-blades  with  reference  to  one  another  so 
that  the  greatest  amount  of  leaf  surface  may  be  exposed  to 
direct  illumination.  A  general  mosaic  arrangement  of  leaves 
may  be  observed  in  connection  with  almost  every  broad- 
leaved  plant  (Figs.  165  and  166) ;  and  even  when  the  leaves 


204 


ELEMENTARY   STUDIES   IN   BOTANY 


are  separated  along  an  erect  stem,  a  view  from  above,  in 
which  all  the  leaves  are  referred  to  a  single  plane,  shows 
the  mosaic  arrangement.  In  many  trees  in  dense  forests, 
notably  in  the  tropics,  the  leaves  appear  chiefly  and  some- 
times exclusively  at  the  extremities  of  the  branches,  often 
producing  a  magnificent  dome-like  mosaic. 

In  the  case  of  stems  exposed 
to  direct  light  only  on  one 
side,  as  the  horizontal  branches 
of  trees,  stems  prostrate  on  the 
ground,  and  stems  against  a  sup- 
port (as  climbers  and  twiners),  the 
leaf-blades  are  brought  to  the  light 
side  so  far  as  possible.  Looking 
up  into  a  tree  in  full  foliage,  one 
will  notice  that  the  horizontal 
branches  are  comparatively  bare 
beneath,  the  Leaf-blades  being 
displayed  on  the  upper  side  as 
a  mosaic.  The  most  literal  and 
complete  mosaic  is  shown  by  cer- 
tain ivies,  whose  leaf-blades  are 
so  adjusted  to  light  that  the 
surface  of  a  wall  is  covered  com- 
pletely by  leaf-blades  fitted  to- 
gether in  a  living  mosaic  (Fig. 
167).  The  ivy  mosaic  is  striking  chiefly  because  the  leaf- 
blades  are  all  displayed  in  approximately  a  single  plane. 

124.  Protective  structures.  —  The  protection  most  widely 
needed  by  land  plants  is  against  excessive  loss  of  water,  and 
since  the  leaves  are  the  prominent  transpiring  organs,  the 
chief  methods  of  protection  concern  them.  Drought  is 
usually  accompanied  by  intense  light,  which  is  also  danger- 
ous to  the  chloroplasts.  The  problem  of  drought  is  pre- 
sented to  plants  in  three  aspects :  (1)  the  possible  drought, 


FIG.  168.  —  Section  through  a  small 
portion  of  a  carnation  leaf,  show- 
ing epidermis  overlaid  by  a  very 
heavy  cuticle  ;  a  single  stoma  in 
the  epidermis,  opening  without 
into  a  tubular  passageway 
through  the  cuticle,  and  within 
into  an  air-chamber  ;  below  are 
the  mesaphyll  cells  containing 
chloroplasts. 


LEAVES 


205 


which  may  occur  at  any  time  or  not  at  all ;  (2)  the  periodic 
drought,  which  is  a  regular  season  of  the  year ;  (3)  the  per- 
petual drought,  which  characterizes  arid  regions,  such  as 
the  states  on  the  Mexican  border.  It  is  evident  that  the 
ordinary  crop-producing  regions  of  this  country  come  under 
the  first  head,  and  that  a  possible  drought  is  the  hardest 
kind  to  provide  against.  When  there  is  a  regular  period  of 
drought,  the  life-histories  of  plants  become  adjusted  to  it, 


PIG.  169.  —  Sections  through  leaves  of  the  same  plant,  showing  the  effect  of  exposure 
to  light  upon  the  structure  of  the  mesophyll :  A,  leaf  exposed  to  intense  sunlight ; 
B,  leaf  grown  in  the  shade.  —  After  STAHL. 

just  as  to  a  winter  period ;  when  there  is  perpetual  drought, 
only  those  plants  equipped  for  it  succeed  in  living,  or  it  is 
controlled  by  irrigation ;  but  when  drought  comes  at  irregu- 
lar intervals,  it  is  usually  a  question  of  the  endurance  of  poorly 
equipped  plants.  The  subject  of  protection  is  too  large  and 
complex  to  be  presented  with  any  completeness,  and  there- 
fore a  few  illustrations  of  protection  that  seem  to  be  de- 
finite must  suffice. 

In  the  description  of  the  structure  of  leaves  attention  was 
called  to  the  fact  that  the  epidermis  with  its  layer  of  cuticle 
is  an  ever-present  check  against  transpiration.  Of  course 


206 


ELEMENTARY   STUDIES   IN   BOTANY 


the  epidermis  is  always  present,  but  the  amount  of  cuticle 
(Fig.  158)  may  vary  widely.     It  is  in  plants  of  dry  regions 

that  the  cuticle  may 
become  very  thick, 
layer  after  layer  being 
added  to  it  by  the 
epidermal  walls  be- 
neath. In  some  cases 

the       cutjcle 

SO  thick   that   the 

,  ,     . 

SRgewayS  through  it  to 

the  stomata  resemble 

short  tubes  (Fig.  168),  the  stomata  being  said  to  be  "  sunken." 
The  layer  of  palisade  cells  (Fig.  157),  which  is  developed 


FIG  170.  -  Section  through  the  leaf  of  bush  clover, 
showing  the  usual  leal  structure,  and  also  the 
numerous  simple  hairs  produced  by  the  lower 
epidermis  ;  observe  that  the  hairs  bend  sharply 
and  lie  along  the  surface  of  the  leaf. 


FIG.     171.  —  Branching    hair    of      FIG.  172.  —  Scale  from  the  leaf  of  Shepardia ;   such 
mullein.  scales  overlap  and  form  a  complete  covering. 

in   leaves   whose   two   surfaces   are   unequally   illuminated, 
must  tend  to  diminish  transpiration  by  exposing  only  the 


LEAVES 


207 


ends  of  elongated  cells  which  stand  so  close  together  that 
there  is  no  drying  air  between  them.  It  seems  probable, 
however,  that  palisade  development  has  more  to  do  with  the 
intensity  of  light  than  with  drought.  Figure  169  shows  in 
a  striking  way  the  effect  of  different  light  intensities  upon 
the  structure  of  the  mesophyll  of  leaves  of  the  same  plant. 
It  has  been  observed  that  the  chloroplasts  are  able  to  assume 
various  positions  in  cells,  in  very  intense  light  moving  to  the 
more  shaded  depths  of  palisade  cells,  and  in  less  intense 
light  moving  to  the  more  ex- 
ternal regions  of  the  cells. 

Hairs  and  scales  are  very 
common  outgrowths  from 
the  epidermal  cells  of  leaves 
and  stems  (Figs.  170-172), 
and  it  is  natural  to  associate 
them  with  the  idea  of  pro- 
tection of  some  kind.  But 
they  are  not  related  to 
drought  or  to  intense  light 
definitely  enough  to  make  it 
clear  that  they  are  a  pro- 
tection against  these  dangers, 
hairy  plants  are  characteristic  of  dry  regions,  and  also  that 
a  covering  of  hairs  is  an  effective  sun  screen  in  regions  of 
intense  light,  but  there  also  are  many  hairy  plants  in  moist 
and  well-shaded  forests. 

Small  leaves  are  also  characteristic  of  dry  regions,  and  it 
is  easy  to  see  that  a  small  leaf  exposes  a  small  surface  to  the 
drying  air  and  the  intense  light,  but  the  total  leaf  exposure 
on  a  plant  may  not  be  reduced.  That  the  reduction  in  size 
holds  a  direct  relation  to  the  dry  conditions  is  evident  from 
the  fact  that  the  same  plant  often  produces  small  leaves  in 
dry  conditions  and  larger  ones  in  moist  conditions,  but  this 
is  more  evidently  a  response  to  conditions  for  growth  than, 
an  effort  to  check  transpiration. 


FIG.  173.  —  Section  through  a  leaf  of 
Begonia,  showing  epidermal  layers  (e)t 
water  storage  tissue  (w),  and  the  cen- 
tral cells  containing  chloroplasts  (c). 


It  has  been  suggested  that 


208 


ELEMENTARY    STUDIES   IN   BOTANY 


The  most  notable  protective  structure  in  plants  of  dry 
regions,  aside  from  the  ever-present  epidermis  and  cuticle, 
is  the  water  storage  tissue.  This  is  not  a  protection  against 
loss  of  water,  but  the  same  end  is  accomplished  by  storing 
water.  Usually  the  water  reservoir  is  a  definite  tissue, 
often  being  distinguished  from  the  green  working  cells  in 
leaves  by  being  a  group  of  colorless  cells  (Fig.  173.)  In 


FIG.  174.  —  Agave  (maguey),  showing  rosette  of  fleshy  leaves.  —  Photograph  by  LAND 
near  San  Luis  Potosi,  Mexico. 


regions  of  perpetual  drought,  the  leaves  may  become  thick 
and  fleshy  on  account  of  extensive  water  storage  tissue,  as 
in  the  agave  (Fig.  174).  In  the  cactus  the  leaves  have  been 
abandoned  as  foliage  organs,  and  the  peculiar  stems  have 
become  great  reservoirs  of  water.  The  globular  body,  so 
common  a  cactus  form  (Fig.  175),  may  be  taken  to  represent 
the  form  of  body  by  which  the  least  amount  of  surface  may  be 
exposed  and  the  greatest  amount  of  water  storage  secured. 
In  the  case  of  these  fleshy  leaves  and  bodies,  it  has  long  been 


LEAVES  209 

noticed  that  they  not  only  contain  water,  but  also  have  great 
power  of  retaining  it. 

The  need  of  protection  against  drought  and  intense  light 
is  probably  obvious  to  every  one,  but  that  leaves  need  to  be 
protected  against  rain  is  not  often  considered.  Rain  falling 
upon  plants  is  felt  to  be  a  blessing  rather  than  a  menace,  and 
so  it  is  if  the  leaves  are  protected  properly.  If  the  water 


FIG.  175.  —  A  globular  cactus.  —  Photograph  by  LAND  near  Tehuacan,  Mexico;   note 
the  coin  (a  dollar)  fastened  to  the  base,  to  indicate  the  size  of  the  plant. 

soaks  into  the  leaves  and  fills  up  the  air-spaces,  replacing  the 
internal  atmosphere,  the  communication  of  the  working  cells 
with  the  external  atmosphere  is  cut  off.  This  would  be  as 
dangerous  to  the  leaf  as  if  water  should  replace  the  internal 
atmosphere  in  a  man's  lungs  ;  in  other  words,  the  leaf  would  be 
drowned.  The  impression  that  leaves  take  in  water  when  it 
rains  is  doubtless  due  to  the  common  observation  that  when 
wilted  leaves  are  sprinkled  they  "  revive,"  the  inference  being 
that  the  sprinkled  water  has  passed  into  the  leaves.  The 


210 


ELEMENTARY    STUDIES   IN   BOTANY 


leaves  have  wilted  because  they  have  been  losing  water  at  a, 
more  rapid  rate  than  it  has  been  supplied  to  them,  and  the 
effect  of  the  sprinkling  is  to  check  this  loss  by  developing  a 
moist  atmosphere  about  the  leaves,  so  that  it  shall  not  exceed 

the  supply  that  is  coming  from 
the  roots.  In  other  words, 
sprinkling  provides  a  dam 
against  water  loss,  and  allows 
water  to  accumulate  again  in 
the  leaves ;  so  that  the  water 
that  "  revives  "  wilted  leaves 
is  not  that  which  is  sprinkled, 
but  that  which  is  coming  all 
the  time  from  the  roots  and  is 
now  allowed  to  accumulate 
a  little. 

Some  of  the  structures  that 
prevent  the  rain  from  soak- 
ing in  are  a  smooth  epidermis, 
a  cuticle,  a  waxy  deposit,  felt- 
like  coverings  of  hairs,  over- 
lapping scales  (like  shingles 
on  a  roof),  etc.  In  the  rainy 
tropics,  where  this  danger  is 
extreme,  it  is  very  common 
for  the  sunken  veins  and  ribs 
of  the  leaves  to  form  a  sort 


FIG   176.  —  A  leaf  of  a  rainy  tropical    of  drainage  system  for  carry- 

forest,    with     a     drainage     system     of 
sunken  veins  and    i 
—  After  SCHIMPER. 


spout-like    point. 


ing     off     water,     the     main 
channel  lying  along  the  mid- 
rib, which  terminates  in  a  long  spout-like  point  (Fig.  1.76). 

125.  Protective  positions.  —  Leaves  are  protected  against 
drying  air  and  intense  light  not  only  by  their  structures,  but 
often  also  by  their  positions,  and  such  plants  are  unusually 
well-equipped  to  endure  exposure. 


LEAVES 


211 


Perhaps  the  most  common  method  of  protection  used  by 
small  plants  growing  in  exposed  situations,  as  bare  rocks  and 
sandy  soil,  is  the  rosette-habit  (§  123,  p.  200)  (Figs.  163  and  164). 
The  clustered  leaves,  flat  upon  the  ground  or  nearly  so,  and 
more  or  less  overlapping,  form  a  very  effective  arrangement 
for  resisting  intense  light  or  drought ;  but  it  must  be  remem- 
bered that  it  is  not  an 
effective  arrangement  of 
leaves  for  work,  it  is  only 
an  effective  arrangement 
for  protection,  so  that 
work  may  go  on  in  un- 
favorable conditions. 

A  position  developed 
by  the  leaves  of  some 
plants  in  regions  of  in- 
tense light  is  the  profile 
position,  and  such  leaves 
are  called  profile  leaves, 
a  margin  being  directed 
upwards  and  the  leaves, 
in  this  way,  standing 
edgewise.  This  position 
results  in  turning  away 
the  faces  of  the  leaves 
from  the  intense  rays  of 

.  ,  ,  ,  .  FIG.  177.  —  Prickly  lettuce,  showing  the  profile 

midday       and        exposing  (edgewise)  leaves  from  two  points  of  view. 

them  to  the  morning  and 

evening  rays  of  less  intensity.  In  the  dry  regions  of  Australia 
the  leaves  of  many  of  the  forest  trees  and  shrubs  are  profile 
leaves,  giving  to  the  foliage  a  very  peculiar  appearance.  The 
best  known  illustration  of  a  plant  in  this  country  with  profile 
leaves  is  the  "  compass  plant,"  a  rosinweed  of  the  prairie 
region.  Its  name  was  given  because  its  edgewise  leaves  were 
observed  to  point  in  a  general  north  and  south  direction, 


212 


ELEMENTARY   STUDIES   IN   BOTANY 


serving  the  purpose  of  a  compass.  It  was  actually  thought, 
for  a  time,  that  the  direction  of  these  leaves  is  controlled  in 
some  mysterious  way  by  magnetic  influence ;  but  it  is  evident 
that  the  plane  of  a  profile  leaf,  exposing  its  faces  to  the  morn- 
ing and  evening  sun,  will  lie  in  a  general  north  and  south 
direction.  In  other  Words,  the  leaves  point  north  and  south 
because  the  sun  rises  in  the  east  and  sets  in  the  west.  It  is 
a  significant  fact  that  compass  plants  grown  in  the  shade  do 
not  develop  profile  leaves.  It  must  not  be 
supposed  that  there  is  anything  like  accuracy  in 
the  north  and  south  direction  of  a  profile  leaf. 


FIG.  178. —  Leaf  of  sensitive  plant  in  two  conditions :  A,  fully  expanded,  with  the  four 
main  branches  and  numerous  leaflets  well  spread ;  B,  after  a  shock  of  some  kind, 
the  leaflets  having  been  thrown  together  forward  and  upward,  the  four  branches 
having  been  moved  toward  each  other,  and  the  main  petiole  having  dropped  sharply 
downward.  —  After  DUCHARTRE. 

It  may  be  the  prevailing  general  direction  of  the  profile 
leaves  of  the  rosinweed  referred  to,  but  in  the  prickly 
lettuce  (Fig.  177),  a  very  common  weed  of  waste  grounds 
even  in  cities,  and  one  of  the  most  striking  of  the  compass 
plants,  the  profile  position  is  frequently  assumed  without 
any  reference  to  the  north  or  south  direction  of  the  apex. 

Still  more  specialized  are  the  motile  leaves,  which  have  the 
power  of  shifting  their  position  according  to  the  needs,  direct- 
ing their  flat  surfaces  towards  the  light,  or  more  or  less 


LEAVES 


213 


inclining   them.      Such   leaves   have   been   developed  most 
extensively  in  the  pea  family,  and  the  most  conspicuous  illus- 


FIG.  179.  —  The  day  (A)  and  night  (B)  positions  of  the  leaves  of  a  clover-like  plant. 
—  After  STRASBURGER. 

trations  are  the  "  sensitive  plants  "  of  the  drier  regions.  The 
name  has  been  given  because  the  leaves  respond  to  various 
stimuli  by  changing  position  with 
remarkable  rapidity.  A  slight  touch, 
or  even  jarring,  will  call  forth  a 
response  from  the  leaves,  and  the 
sudden  application  of  heat  gives 
striking  results.  The  leaves  of  the 
best  known  sensitive  plant  (Fig. 
178)  are  divided  into  very  numer- 
ous small  leaflets,  which  stand  in 
pairs  along  the  leaf  branches. 
When  a  drought  begins,  some  pairs 
of  leaflets  come  together  face  to 
face,  slightly  reducing  the  surface 
exposure.  If  the  drought  continues, 
more  leaflets  come  together,  then 
still  others,  until  finally  all  the 
leaflets  may  be  in  contact  in  pairs,  and  the  leaves  them- 
selves may  droop  against  the  stem.  In  this  way  the  ex- 
posed surface  may  be  regulated  according  to  the  need,  on 
15 


FIG.  180.  —  Diagrammatic  sec- 
tion through  a  node  of  horse 
chestnut,  showing  the  posi- 
tion of  the  cutting-off  layer 
(s)  and  the  vascular  bundle 
(b)  not  cut  through. 


214 


ELEMENTARY   STUDIES   IN   BOTANY 


the  same  principle  that  a  sailing  vessel  may  regulate  its 
sail-exposure  according  to  the  need.  Motile  leaves  also  shift 
their  positions  throughout  the  day  in  reference  to  light; 
and  at  night  a  very  characteristic  position  is  assumed,  once 
called  a  "  sleeping  "  position,  but  better  called  a  night  posi- 
tion. The  contrast  between  the  day  and  night  positions  of 

many  leaves,  even  clover 
leaves  (Fig.  179),  is  quite 
striking.  These  night  posi- 
tions may  be  induced  ex- 
perimentally by  placing 
plants  in  darkness. 

126.  The  fall  of  leaves.  - 
Many  shrubs  and  trees  of 
temperate  regions  lose  their 
leaves  every  year,  usually 
at  the  approach  of  winter, 
putting  out  new  leaves  in 
the  following  spring.  This 
is  called  the  deciduous  habit, 
and  such  trees  are  called 
deciduous  trees.  While  in 
some  deciduous  trees,  as  the 
oaks,  there  is  no  special 
preparation  for  " shedding" 
leaves,  in  most  of  them  a 
special  plate  of  cells  is  formed 

near  the  juncture  of  the  leaf  with  the  stem,  known  as  the  "  cut- 
ting-off  layer,"  which  gradually  separates  the  leaf  from  the 
stem,  so  that  it  falls  by  its  own  weight  or  is  wrenched  off  by 
the  wind  (Fig.  180). 

In  connection  with  the  deciduous  habit  there  often  appears 
the  autumnal  coloration  of  leaves,  so  striking  a  feature  of 
temperate  forests.  The  colors  that  appear  are  shades  of 
yellow  and  red,  either  pure  or  variously  intermixed.  They 


FIG.  181.  —  A  pine  twig,  showing  the 
needle-leaves,  and  a  cluster  of  stami- 
nate  cones.  —  Photograph  by  LAND. 


LEAVES 


215 


are  the  result  of  the  waning  activity  of  the  leaf,  the  yellow 
mostly  being  the  color  of  the  dying  chloroplasts,  and  the  red 
coming  from  the  presence  of  a  new  substance  produced  in  the 
enfeebled  cells.  The  popular  belief  that  these  colors  are 
caused  by  frost  is  only  partly  true,  for  they  often  appear 
before  there  has  been  any  frost ;  but  they  may  be  induced  by 
any  conditions  that  tend  to  diminish  the  activity  of  the  leaf, 
and  cold  is  one  of  the  conspicuous  conditions. 

In  contrast  with  the  deciduous  shrubs  and  trees  are  the 
so-called  "  evergreens," 
in  which  there  is  no  regu- 
lar annual  fall  of  leaves. 
Such  leaves  endure  for  a 
varying  length  of  'time, 
but  as  there  is  no  regular 
period  for  all  of  them,  the 
shrub  or  tree  always  ap- 
pears in  foliage.  In  the 
temperate  regions,  the 
most  conspicuous  ever- 
greens are  the  pines  and 
their  allies.  A  compari- 
son between  the  needle- 
leaf  of  a  pine  (Fig.  181) 
deciduous  tree  will  show 


FIG.  182.  —  Cross-section  of  a  pine  needle,  show- 
ing epidermis  with  sunken  stomata,  groups 
of  heavy-walled  cells  beneath  epidermis,  the 
mesophyll  (the  cells  characterized  by  curious 
infolded  walls)  containing  seven  resin  canals, 
and  the  central  vascular  region  containing 
two  bundles  (xylem  uppermost). 


and 
what 


the  leaf  of  an  ordinary 
the  evergreen  habit  in- 
volves in  temperate  regions.  The  pine  leaf  must  be 
protected  so  as  to  endure  the  winter,  and  this  has  in- 
volved reduction  in  surface  and  extremely  thick  protec- 
tive layers  about  the  mesophyll  (Fig.  182).  This  ha& 
diminished  the  ability  to  work,  but  it  has  saved  the  tree  the 
necessity  of  putting  out  a  complete  new  crop  of  leaves  for 
the  next  season.  In  other  words,  the  cost  of  the  winter  pro- 
tection of  leaves  is  a  loss  of  working  power  during  the  spring 
and  summer.  The  deciduous  leaf,  on  the  other  hand,  is 
broad  and  thin,  with  great  capacity  for  work ;  but  this  for- 


216 


ELEMENTARY   STUDIES   IN   BOTANY 


bids  protection  during  the  winter.  It  is  merely  a  balancing 
between  protection  and  work;  the  evergreens  lay  emphasis 
on  protection,  and  the  deciduous  plants  on  work. 

127.  Special  forms  of  leaves.  —  We  have  been  considering 
leaves  as  foliage,  but  in  many  cases  they  are  so  modified  that 
they  either  lose  their  character  as  machines  for  the  manufac- 
ture of  carbohydrate  food,  or  add 
to  it  some  other  work.  In  so  far 
as  they  remain  green,  they  manu- 
facture carbohydrates  as  do  the 
foliage  leaves,  but  a  definite  change 
in  structure  and  behavior  indicates 
that  they  are  constructed  for  some 
other  kind  of  work  also.  This 
subject  is  a  very  extensive  one,  so 
that  only  some  of  the  conspicuous 
illustrations  will  be  noted. 

In  certain  situations  leaves  are 
not  free  to  develop  to  full  size, 
and  when  this  happens  they  may 
not  develop  chloroplasts,  so  that 
they  do  not  even  become  green. 
Such  leaves  are  called  scales.  They 
are  often  called  " reduced"  leaves, 
but  they  have  not  been  reduced 
from  a  larger  size  ;  they  have  never 
developed  to  a  larger  size.  The 
most  conspicuous  illustrations  of 

scales  are  found  among  plants  with  subterranean  stems 
and  in  connection  with  " scaly"  buds.  One  of  the  features 
of  a  stem  is  to  produce  leaves,  but  underground  stems 
cannot  produce  foliage  leaves  unless,  as  in  ferns,  the  leaves 
reach  the  surface  and  develop  in  the  light.  When  they 
do  not  reach  the  surface,  the  leaves  appear  as  small  scale-like 
bodies  without  green  tissue.  Often  these  scales  seem  to  be 


FIG.  183.  —  Pinnately  compound 
leaf  of  garden  pea,  whose  ter- 
minal portion  has  developed 
as  tendrils.  —  After  STRAS- 

BURGER. 


LEAVES 


217 


merely  useless  relics,  but  sometimes  they  are  used  for  food 

storage,  as  in  lily  bulbs,  onions,  etc.,  which  are  mostly  made 

up  of  fleshy  scales.     In  the  scaly  buds,  so  common  on  shrubs 

and  trees,  the  leaves  are  prevented  from  developing  by  being 

kept  close  together,  so  that  they  overlap.     These  overlapping 

bud  scales  are  clearly 

useful    as    protective 

structures,  and  to  this 

end  they  are  generally 

firm     and     resistant, 

often  coated  with 

resin,    and    the  inner 

ones    frequently 

clothed     with   woolly 

hairs. 

Leaves  may  some- 
times develop  as  ten- 
drils, either  the  whole 
leaf  or  some  of  its 
branches  becoming 
tendrils,  as  in  the  sweet 
pea  (Fig.  183).  Ten- 
drils are  peculiarly 
sensitive  to  contact, 
and  the  resulting  cur- 
vature grips  the  body 
touched,  and  a  suc- 
cession of  tendrils  thus 
enables  a  plant  to 
"  climb." 

Leaves  are  sometimes  developed  as  thorns,  as  may  be  ob- 
served in  the  barberry  (Fig.  184),  or  sometimes  only  certain 
regions  of  the  leaf  become  thorns,  as  in  the  common  locust, 
acacia,  etc. 

The  most  singular  use  of  leaves,  however,  is  for  catching, 


FIG.  184.  —  Leaves  of  barberry  developing  as  thorns. 


218 


ELEMENTARY   STUDIES   IN   BOTANY 


insects.  Plants  with  such  leaves  are  often  called  "  carnivo- 
rous plants  "  or  "  insectivorous  plants/'  since  the  captured 
insects  are  used  for  food.  This  is  merely  one  way  of  getting 
protein  food  without  manufacturing  it,  and  at  the  same  time 
such  leaves  are  usually  green  and 
manufacture  their  carbohydrate 
food.  Three  conspicuous  illus- 
trations of  insect-catching  leaves 
will  be  given. 

The   "  pitcher-plants  "   are   so 


FIG.  185.  —  Leaves  of  the  common  northern 
pitcher-plant,  one  of  them  cut  across  to 
show  cavity  and  wing.  —  After  GRAY. 


FIG.  186.  —  Leaf  of  a  southern 
pitcher-plant,  showing  the  fun- 
nel form  and  winged  pitcher, 
and  the  overarching  hood  with 
translucent  spots.  —  After 
KEENER. 


named  because  the  leaves  form  tubes  or  urns  of  various 
forms,  which  contain  water,  and  to  these  pitchers  insects 
are  attracted  and  then  drowned.  The  common  pitcher- 


LEAVES 


219 


plant  of  the  northern  states  (a  Sarracenia)  is  a  well- 
known  bog  plant  (Fig.  185),  but  it  is  not  so  elaborately 
constructed  for  capturing  insects  as  is  a  common  south- 
ern Sarracenia  (Fig.  186).  In  this  plant  the  leaves  are 
slender,  hollow  cones,  and  rise  in  a 
tuft  from  the  swampy  ground.  The 
mouth  of  this  conical  urn  is  overarched 
and  shaded  by  a  hood,  in  which  are 


FIG.  187.  —  Leaves  of  the  Californian  pitcher-plant, 
showing  the  twisted  and  winged  pitcher,  the 
overarching  hood  with  translucent  spots,  and  the 
fish-tail  appendage  to  the  hood.  —  After  KEENER. 


FIG.  188.  —  Leaf  of  Nepen- 
thes, showing  the  blade- 
like  base,  the  tendril 
portion,  and  the  termi- 
nal pitcher  with  its  lid. 
—  After  GRAY. 


translucent  spots,  like  numerous  small  windows.  Around 
the  mouth  of  the  urn  are  glands  which  secrete  a  sweet 
liquid  (nectar).  Inside,  just  below  the  rim  of  the  urn,  is 
a  glazed  zone,  so  smooth  that  insects  cannot  walk  upon 


220 


ELEMENTARY   STUDIES   IN   BOTANY 


it.  Below  the  glazed  zone  is  another  one  thickly  set 
with  stiff,  downward-pointing  hairs;  and  below  this  is 
the  liquid  in  the  bottom  of  the  urn.  If  a  fly,  attracted 
to  the  nectar  at  the  rim  of  the  urn,  attempts  to  descend 
within  the  urn,  it  slips  on  the  glazed  zone  and  falls  into 
the  water;  and  if  it  attempts  to  escape  by  crawling,  the 
downward-pointing  hairs  prevent.  If  it  seeks  to  fly  from 

the  rim,  it  naturally 
flies  towards  the  trans- 
lucent spots  in  the  hood, 
since  the  direction  of  en- 
trance is  in  the  shadow  ; 
and  pounding  against 
the  hood,  the  fly  usu- 
ally falls  into  the  tube. 
The  pitchers  usually 
contain  the  decaying 
bodies  of  numerous 
drowned  insects.  A 
much  larger  Californian 
pitcher-plant  is  Darling- 
tonia,i(Fig.  187),  whose 
leaves  are  one  and  a  half 
to  three  feet  high,  the 
hood  bearing  a  gaudily 
colored  " fish-tail"  ap- 
pendage, the  whole  structure  being  a  more  elaborate  in- 
sect trap  than  are  the  leaves  of  Sarracenia.  In  these 
traps  not  only  are  the  remains  of  flies  found,  but  bees, 
hornets,  butterflies,  beetles,  grasshoppers,  and  even  snails 
have  been  reported.  The  species  of  Nepenthes,  from  the 
oriental  tropics,  very  common  in  conservatories,  develop 
most  remarkable  leaves,  the  lowest  part  being  an  ordinary 
blade,  beyond  which  is  a  well-developed  tendril,  at  the  end  of 
which  there  arises  an  elaborate  pitcher  with  a  lid  (Fig.  188). 


FIG.  189.  —  Sundews.  —  After  KEENER. 


LEAVES 


221 


There  is  the  same  sweetish  secretion  at  the  rim  of  the  pitcher, 
and  the  same  accumulation  of  water  within  as  in  the  ordinary 
pitcher-plants. 

The  "  sundews  "  are  forms  of  Drosera,  and  grow  in  swampy 
regions,  the  leaves  forming  small  rosettes  upon  the  ground 
(Fig.  189).  In  one  form  the  blade  is  round,  and  the  margin  is 
beset  by  prominent  bristle-like  hairs,  each  with  a  globular 


FIG.  190.  —  Two  leaves  of  a  sundew:  A,  glandular  hairs  fully  extended;  B,  half  the 
hairs  bending  inward,  in  position  assumed  when  an  insect  has  been  captured.  — 
After  KERNER. 


gland  at  its  tip  (Fig.  190).  Shorter  gland-bearing  hairs  are 
scattered  also  over  the  inner  surface  of  the  blade.  All  these 
glands  excrete  a  clear,  sticky  fluid,  which  clings  to  them  like 
dewdrops,  and  which,  not  being  dissipated  by  sunlight,  has 
suggested  the  name  sundew.  If  a  small  insect  becomes  en- 
tangled in  one  of  the  sticky  drops,  the  hair  begins  to  curve  in- 
ward, and  presently  presses  its  victim  down  upon  the  surface 
of  the  blade.  In  the  case  of  a  larger  insect,  several  of  the 
marginal  hairs  may  join  together  in  holding  it,  or  the  whole 
blade  may  become  more  or  less  rolled  inward. 


222 


ELEMENTARY    STUDIES   IN   BOTANY 


The  "  Venus  fly-trap  "  (Dioncea)  is  one  of  the  most  famous 
and  remarkable  of  insect-trapping  plants,  being  found  only 
in  certain  sandy  swamps  near  Wilmington,  N.  C.  The  leaf- 
blade  is  constructed  so  as  to  work  like  a  steel  trap,  the  two 
halves  snapping  together  and  the  marginal  bristles  interlock- 
ing like  the  teeth  of  a  trap  (Fig.  191).  A  few  sensitive  hairs, 
like  feelers,  are  developed  on  the  leaf  surface ;  and  when  one 

of  these  is  touched  by  a 
small  flying  or  hovering 
insect,  the  trap  snaps  shut 
and  the  insect  is  caught. 
Only  after  digestion,  which 
is  a  slow  process,  does  the 
trap  open  again. 

128.  Summary.  —  Leaves 
are  essentially  expansions 
of  green  tissue  organized 
for  the  work  of  photosyn- 
thesis, and  therefore  exposed 
to  light  and  air.  The  vari- 
ations in  the  forms  and 
superficial  structure  of 
leaves  are  extremely  numer- 
ous, but  the  essential  struct- 
ure comprises  an  epidermis 
which  protects  the  working 
cells  against  excessive  loss 

of  water,  a  mesophyll  region  which  is  made  up  of  the  green 
working  cells,  and  veins  which  distribute  water  among  the 
working  cells.  The  expanded  form  of  the  leaf  is  maintained 
by  the  comparatively  rigid  framework  of  veins,  and  by  the 
turgor  of  the  mesophyll  cells. ' 

The  necessary  relations  of  leaves  to  light  involve  adjust- 
ments to  prevent  an  excessive  shading  of  leaves  by  one  an- 
other. The  most  general  statement  of  the  situation  is  that 


FIG.  191.  —  Three  leaves  of  Dioncea:  two 
with  the  traps  open,  one  with  trap  shut 
on  an  insect.  —  After  KERNER. 


LEAVES  223 

the  leaves  of  a  plant  are  so  adjusted  to  one  another  that  they 
form  a  mosaic. 

The  necessary  exposure  of  leaves  to  the  light  involves  the' 
corresponding  danger  of  excessive  transpiration.  The  pro- 
tective structures  against  the  danger  of  transpiration  are 
chiefly  the  epidermis  with  its  cuticle,  the  palisade  layer,  and 
water-storage  tissue.  The  plants  further  equipped  for  pro- 
tection by  the  position  of  their  leaves  are  those  which  have  the 
rosette  habit,  or  profile  leaves,  or  motile  leaves. 

While  foliage  leaves  may  be  regarded  as  representing  the 
usual  leaf,  they  may  be  replaced  by  structures  that  do  not 
have  the  appearance,  nor,  in  many  cases,  the  function  of  foli- 
age leaves.  Such  replacing  structures  are  called  " modified" 
leaves  chiefly  because  they  appear  in  the  position  usually 
occupied  by  leaves. 


CHAPTER  XII 

STEMS 

129.  General   character.  —  A   stem   is   characterized   by 
bearing  leaves,  and  this  involves  two  problems :    (1)  the  dis- 
play of  leaves,  and  (2)  the  conduction  of  water.     Stems  are 
not  always  rigidly  erect,  for  they  may  be  prostrate  or  climb- 
ing ;   neither  are  they  always  aerial,  for  many  stems  are  sub- 
terranean.    Often  stems  are  unbranched  (simple),  in  which 
case  the  leaf  display  is  relatively  small ;    often  they  are 
branched,  which  simply  means  an  increased  capacity  for  leaf 
display,  which  reaches  its  maximum  in  certain  types  of  trees. 

What  is  called  the  habit,  that  is,  the  general  appearance  of 
a  plant,  is  determined  by  the  character  of  the  stem,  the  leaves 
being  a  constant  feature  in  every  case.  For  example,  trees 
are  recognized  in  winter  by  their  stem  habit  as  easily  as  when 
they  are  in  foliage. 

130.  Leaf  display.  —  There  are  some  general  facts  about 
the  display  of  leaves  by  aerial  stems  that  should  be  recognized. 
The  stem  (or  branch)  of  a  seed-plant  does  not  produce  leaves 
indiscriminately  throughout  its  whole  length,   but  only  at 
certain  definite  regions  called  the  nodes,  the  regions  between 
the  nodes  being  called  internodes.     This  means  that  the  stem 
is  differentiated  into  two  regions,  the  nodes  that  produce 
leaves  and  the  internodes  that  do  not,  and  these  two  regions 
differ  also  in  structure.     The  significance  of  this  differentia- 
tion is  that  while  the  nodes  are  constructed  to  produce  leaves, 
the  internodes  are  constructed  to  elongate,  so  that  the  leaves 
are  separated.     Plants  vary  in  the  amount  of  the  separation  of 

224 


STEMS 


225 


FIG.   192.  —  A   scarlet   runner   bean,  showing   leaf- 
bearing  nodes,  internodes,  and  axillary  branches. 


their  leaves,  and  this 
is  a  measure  of  the 
power  of  the  inter- 
nodes  to  elongate.  It 
is  evident  that  leaves 
separated  by  the  inter- 
nodes  to  such  an  ex- 
tent that  they  do  not 
shade  one  another  are 
in  the  most  favorable 
condition  for  work. 

In  such  a  stem,  the 
leaves  begin  to  form  before  the  internodes  begin  to  elongate, 
so  that  the  young  leaves  are  packed  together  in  the  structure 

called  a  bud;  that  is,  a  leaf- 
bud  as  distinct  from  a  flower- 
bud.  When  the  internodes 
begin  to  elongate,  the  bud  is 
said  to  "  open,"  and  this 
opening  goes  on  until  all 
appearance  of  a  bud  is  lost. 
While  the  bud  is  opening  the 
young  leaves  become  more 
free  and  continue  their  de- 
velopment, so  that  when  the 
internodes  have  reached  their 
full  length,  the  young  stem 
(or  branch)  bears  developed 
leaves,  and  the  plant  is  said 
to  be  "in  foliage."  The  pic- 
ture of  leaves  developing  on 
a  stem,  therefore,  is  not  that 

of  an  elongating  stem  putting  out  leaves,  but  that  of  an 
elongating  stem  separating  growing  leaves  that  have  been 
"put  out"  by  the  nodes. 


FIG.  193.  —  The  so-called  "wedding 
smilax,"  showing  branches  that  re- 
semble leaves  arising  from  the  axils  of 
minute  scales  that  are  the  real  leaves. 


226 


ELEMENTARY   STUDIES   IN   BOTANY 


The  nodes  not  only  produce  leaves,  but  if  the  stem  branches, 
the  nodes  produce  the  branches  also.  It  has  long  been  ob- 
served that  a  branch  arises  at  a  node  immediately  above  a 
leaf,  that  is,  in  the  upper  angle  between  leaf  and  stem,  which 
is  called  the  axil  of  the  leaf  (Fig.  192).  This  usual  relation 
of  branches  to  leaves  is  merely  a  relation  of  position,  which  is 
determined  by  the  fact  that  nodes  are  constructed  to  produce 


FIG.  194.  —  The  arrangement  of  leaves:    A,  spiral  or  alternate  leaves;    B,  opposite 
(cyclic)  leaves ;    C,  whorled  (cyclic)  leaves.  —  After  GRAY. 


"  lateral  members,"  which  in.  this  case  are  leaves  and 
branches.  Why  branches  do  not  usually  appear  between 
leaves  or  below  them  is  a  matter  of  detail  that  does  not  con- 
cern us  here.  However,  it  is  so  usual  for  a  branch  to  arise 
from  the  axil  of  a  leaf  that  this  relative  position  is  often  used 
in  determining  the  nature  of  a  structure.  For  example,  a 
structure  that  has  a  branch  in  its  axil,  even  if  it  is  a  tendril  or 
a  thorn,  is  regarded  as  a  leaf;  and  conversely,  a  structure 
that  arises  from  the  axil  of  a  leaf,  even  if  it  is  a  thorn  or  a 


STEMS 


227 


tendril  or  even  a  good  leaf  in  appearance  (Fig.  193),  is  regarded 
as  a  branch.  Since  the  significance  of  a  structure  is  deter- 
mined by  what  it  can  do,  it  makes  little  difference  what  its 


FIG.  195.  —  An  Austrian  pine. 

origin  really  is.     A  tendril  does  the  work  of  a  tendril,  whether 
it  is  a  leaf  or  a  branch  that  has  been  "  modified." 

Plants  differ  as  to  the  number  of  leaves  produced  by  each 
node.     In  very  many  cases  only  a  single  leaf  is  produced  by 


228 


ELEMENTARY   STUDIES   IN    BOTANY 


a  node,  and  then  the  leaf  from  the  next  node  above  does  not 
arise  directly  over  the  leaf  below  (Fig.  194,  A).  If  an  im- 
aginary line  be  drawn  connecting  the  points  on  the  nodes 


FIG.  196.  —  An  elm  in  foliage. 

at  which  successive  leaves  appear,  it  will  form  a  spiral  wind- 
ing about  the  stem.  Leaves  with  bhis  arrangement,  there- 
fore, are  said  to  be  spiral  (also  commonly  called  alternate). 


STEMS 


229 


It  is  evident  that  this  spiral  succession  of  leaves  results  in 
reducing  to  a  minimum  the  shading  of  the  leaves  by  one 
another.  In  other  plants  two  or  more  leaves  appear  at  each 


FIG.  197.  —  An  oak  in  winter  condition. 


node  (Fig.  194,  B  and  C),  and  such  leaves  are  said  to  be  cyclic 
(very  commonly,  two  leaves  at  a  node  are  said  to  be  opposite, 
and  three  or  more  leaves  at  a  node  are  said  to  be  whorled  or 

10 


230  ELEMENTARY   STUDIES   IN   BOTANY 

verticillate) .  In  the  case  of  cyclic  leaves,  the  cycle  of  one 
node  does  not  stand  directly  over  the  cycle  of  the  node  just 
below  it,  but  over  the  spaces  between  the  leaves  below.  All 
these  terms,  however,  need  not  confuse,  for  the  fundamental 
fact  is  that  leaves  appear  at  the  nodes  in  spiral  succession, 
the  so-called  "  spiral  "  or  "  alternate  "  leaves  referring  to  a 
single  spiral  of  leaf  succession  ascending  the  stem  from  node 
to  node,  and  the  so-called  "  cyclic,"  "  opposite,"  "  whorled," 
or  "  verticillate  "  leaves  referring  to  two  or  more  spirals  of 
leaf  succession  ascending  the  stem  from  node  to  node. 


FIG.  198.  —  Prostrate  stem  of  Potentilla. 

131.  Stem-position.  —  It  is  obvious  that  the  ideal  position 
of  a  stem  for  leaf  display  is  a  free  erect  position,  for  leaves 
can  be  displayed  freely  on  all  sides.  Of  course  to  maintain  a 
free  erect  position  is  not  a  simple  mechanical  problem,  and  in 
such  stems  this  problem  must  be  added  to  the  universal  one 
of  water-conduction.  That  erect  aerial  stems  must  be  con- 
structed to  maintain  their  position  becomes  evident  when 
they  are  contrasted  with  erect  submerged  stems.  In  small 
lakes  and  slow-moving  streams  such  submerged  stems  are 
commonly  seen,  as  the  pickerel-weed  and  numerous  other 
forms.  In  the  water  their  stems  are  erect,  but  when  taken 
out  of  water  they  collapse,  having  been  maintained  in  posi- 
tion by  the  buoyant  power  of  water. 


STEMS 


231 


The  most  impressive  stem  in  relation  to  leaf  display,  both 
in  character  and  amount,  and  also  in  its  construction  for 
maintaining  a  rigidly  erect  position,  is  the  tree.  But  trees 
differ  in  the  completeness  of  provision  for  leaf  display.  In 
some  trees,  as  the  pines  and  their  allies  (Fig.  195),  the  main 
stem  continues  as  a  central  shaft  to  the  top,  the  branches- 
spreading  horizontally  from  it,  resulting  in  a  general  conical 
outline.  In  other  trees,  as  the  elm  (Fig.  196)  and  the  oak 
(Fig.  197),  the  main  stem  soon  divides  into  branches, 
and  there  is  a  great  spreading  top  or  "  crown,"  which 
represents  the  most  complete  provision 
for  a  maximum  amount  of  leaf  surface 
well  displayed. 


FIG.  199.  —  A  strawberry  plant,  showing  a  runner  that  has  de- 
veloped a  new  plant,  which  in  turn  has  sent  out  another 
runner.  —  After  SEUBERT. 


There  are  certain  conditions,  however,  in  which  the  free 
erect  position  of  aerial  stems  is  not  maintained.  In  some 
plants  the  stem  or  certain  of  its  branches  lie  prostrate  on  the 
ground  or  nearly  so,  sometimes  spreading  in  all  directions 
and  becoming  interwoven  into  a  mat  or  carpet  (Fig.  198). 
Such  plants  grow  in  general  on  sterile  and  exposed  soil,  and 
there  may  be  an  important  relation  between  this  fact  and 
their  habit.  A  prostrate  stem  is  in  a  distinctly  disadvantage- 
ous position  foFleaf  display,  for  instead  of  being  free  to 
spread  its  leaves  out  in  all  directions,  the  free  space  for  leaves 
is  diminished  at  least  one-half.  Although  freedom  for  leaf- 
display  is  restricted,  prostrate  stems  are  in  a  very  favorable 


232  ELEMENTARY   STUDIES   IN   BOTANY 

position  for  vegetative  propagation,  and  many  prostrate 
plants  respond  to  the  favoring  conditions.  As  the  prostrate 
stem  advances  over  the  ground,  roots  develop  from  the  nodes 
and  enter  the  soil,  and  a  new  plant  is  started,  which  becomes 
independent  by  the  death  of  the  older  parts  or  by  separation 
from  them.  In  this  way  a  plant  may  spread  over  the  ground, 
multiplying  itself  indefinitely.  A  very  familiar  illustration 
is  furnished  by  the  strawberry  plant,  which  sends  out  pecul- 
iar leafless  branches  called  "  runners/'  which  "  strike  root  " 
at  the  tip  and  start  new  plants  which  become  independent 
by  the  death  of  the  runners  (Fig.  199). 

Prostrate  stems  illustrate  the  fact  that  nodes  can  pro- 
duce not  only  leaves  and  branches,  but  also  roots,  if  placed  in 
suitable  conditions.  Advantage  is  taken  of  this  fact  in  the 
common  process  of  "  layering,"  in  which  such  stems  as  those 
of  blackberries  and  raspberries  are  bent  down  to  the  ground 
and  covered  with  soil,  when  the  covered  nodes  strike  root 
and  new  plants  are  started.  When  any  plants  are  propa- 
gated by  pieces  of  stem,  known  as  "  slips"  or  "cuttings," 
as  in  grape  culture,  it  is  because  nodes  can  develop  roots 
and  thus  make  possible  independent  plants.  The  nodes 
of  some  plants  put  out  roots  when  not  covered  by  soil  or 
even  in  contact  with  soil.  For  example,  the  erect  stem  of 
corn  sends  out  roots  freely  from  the  nodes  near  the  ground, 
and  the  poison-ivy  and  trumpet-creeper  cling  to  supports 
by  tendril-like  roots  produced  by  the  nodes. 

All  that  has  been  said  emphasizes  the  importance  of  nodes, 
which  can  produce  leaves,  stems,  and  roots ;  and  therefore 
a  single  node  from  an  old  plant  may  make  a  new  plant 
possible.  This  is  further  emphasized  in  the  method  of 
propagating  potatoes,  which  are  thickened  subterranean 
stems  called  tubers  (Fig.  217).  It  is  well  known  that  when 
a  tuber  is  cut  in  pieces  for  planting,  each  piece  must  contain 
one  or  more  "  eyes."  An  "  eye  "  is  a  branch  bud  in  the  axil 
of  a  minute  scale-leaf.  There  is  no  special  virtue  in  the  eye 


STEMS 


233 


except  that  it  locates  a  node,  and  it  is  the  node  that  starts 

the  stem  and  root  for  a  new  plant. 

A  third  stem-position  may  be  called  the  climbing  position, 

by  which  a  better  exposure  of  leaves  to  light  may  be  secured 

than  in  a  prostrate  position,  but 
no  more  free  space  for  leaf  dis- 
play, since  the  support  cuts  off 
the  space  for  display  on  one  side. 
In  fact,  a  prostrate  stem  on  ex- 
posed soil  is  about  the  equivalent 


FIG.  200.  —  A  bean  turning  about 
a  support. 


FIG.  201.  —  Branch  of  star-cucumber,  with  its 
tendrils  in  various  conditions. 


of  a  climbing  stem  in  a  dense  forest,  where  climbing  plants 
become  especially  conspicuous,  so  far  as  'leaf  display  is 
concerned. 

132.  Responses  of  climbing  plants.  —  Climbing  stems 
are  often  spoken  of  as  "  twiners  "  and  "  climbers  " ;  in  the 
former  case  the  stem  twining  about  a  support,  as  the  morn- 
ing-glory, bean  (Fig.  200),  hop- vine,  etc. ;  in  the  latter  case 


234 


ELEMENTARY   STUDIES    IN   BOTANY 


tendrils  are  formed  that  either  hook  about  a  support,  as  the 
grape-vine  and  star-cucumber  (Fig.  201),  or  produce  disk- 
like  suckers  at  their  tips  that  act  as  holdfasts  (Fig.  202), 
as  the  woodbine  or  Virginia  creeper  (Fig.  203).  The  twin- 
ing stem  and  the  tendril  exhibit  responses  to  stimuli  that 
should  be  observed. 

If  a  young  morning-glory  or  twining  bean  be  watched 
(Fig.  200),  it  will  be  discovered  that  the  elongating  stem  is 

unable  to  stand  upright,  and 
that,  as  it  bends  over,  the  in- 
clined part  begins  to  swing 
through  a  horizontal  curve, 
which  may  bring  the  stem  in 
contact  with  a  suitable  sup- 
port. If  this  happens,  the 
stem,  continuing  to  swing  in 
a  curve  and  growing  in  length 
at  the  same  time,  winds  itself 
about  the  support.  This 
movement  of  the  portion  of 
the  stem  which  is  in  a  hori- 
zontal position  is  thought  to 
be  brought  about  by  a  pe- 
culiar response  of  the  plant 
to  gravity. 

Tendrils    are    illustrations 
FIG.  202.  —  woodbine  clinging  to  a  wail     of   plant   structures  that  are 

by  means  of  tendril  suckers.  n  • ,  • 

unusually  sensitive  to  con- 
tact. When  the  tip  of  a  tendril  in  moving  about  touches 
a  suitable  support,  the  side  touched  becomes  concave  and 
the  tendril  hooks  or  coils  about  the  support.  This  is 
only  the  first  response  of  the  tendril  to  contact,  for  pres- 
ently the  rest  of  it  begins  to  curve,  a  movement  which 
results  in  spiral  coils,  since  the  tendril  is  fastened  at  both 
ends.  This  curving  and  twisting  of  the  tendril  between 


STEMS 


235 


its  fastened  extremities  naturally  results  in  two  spiral 
coils  running  in  opposite  directions.  In  this  way  the 
stem  is  fastened  to  its  support  by  numerous  spiral  springs. 
All  of  these  movements  and  their  results  may  be  observed 
by  cultivating  a  plant  such  as  the  star-cucumber,  which 
grows  rapidly  and  has  conspicuous  and  very  sensitive  ten- 
drils (Fig.  201).  In  the  case  of  the  ordinary  climbing 


FIG.  203.  —  Woodbine  in  a  deciduous  forest. 

woodbine  and  certain  species  of  ivy,  which  cling  to  walls 
or  tree  trunks,  the  tip  of  the  tendril  when  it  comes  in  contact 
with  a  support  is  stimulated  into  developing  the  disk-like 
sucker  which  acts  as  a  holdfast  (Fig.  202). 

133.  Stem-structure.  —  There  are  two  general  types  of 
stem-structure  exhibited  by  Seed-plants,  one  belonging  to 
the  Gymnosperms  and  Dicotyledons,  and  the  other  to  the 
Monocotyledons.  Since  the  latter  is  only  a  modification 
of  the  former,  the  stem  of  a  Dicotyledon  will  be  used  as  an 
illustration. 


236 


ELEMENTARY   STUDIES   IN   BOTANY 


If  an  active  twig  of  an  ordinary  woody  plant  be  cut  across, 
it  will  be  seen  that  it  is  made  up  of  three  general  regions 

(Fig.  204):  (1)  a  zone  of 
spongy  tissue,  usually  green, 
the  cortex,  and  covered  by  the 


FIG.  205.  —  Cross-section  of 
the  stem  of  a  buttercup 
(an  herb) ,  showing  the  well- 
separated  bundles  that  form 
the  vascular  cylinder,  leav- 
ing broad  pith  rays  ;  observe 
also  the  very  large  pith,  the 
cortex,  the  hairs  arising  from 
the  epidermis,  and  espe- 
cially the  cambium  cells  be- 
tween the  xylem  and  phloem 
and  continuing  across  the 
pith  rays. 


FIG.  204.  —  Cross-section  of  a  branch  of 
box-elder  one  year  old :  c,  cortex ;  w, 
vascular  cylinder ;  p,  pith.  ' 


epidermis ;  (2)  a  relatively  broad  zone  of  firm  wood,  the 
vascular  cylinder;  and  (3)  in  the  center  the  pith.  The 
special  feature  of  this  arrangement  is  that  the  wood  oc- 


FIG.  206.  —  Cross-section  of  vascular  bundle  from  pine  stem,  showing  xylem  (x) , 
cambium  (c),  and  phloem  (p)  ;  on  each  side  of  the  single  row  of  cambium  cells  there 
are  young  xylem  and  phloem  cells  that  pass  gradually  into  the  mature  condition. 

curs  as  a  hollow  cylinder,  inclosing  the  pith  and  sur- 
rounded by  the  cortex.  In  the  older  parts  of  stems  the 
pith  often  disappears,  leaving  a  hollow  stem.  The  cortex 


STEMS  237 

is  the  active  working  region  of  the  stem ;  since  it  is  green 
it  is  able  to  manufacture  carbohydrates  as  do  the  leaves, 
and  it  is  also  concerned  in  other  work  connected  with  nu- 
trition. The  vascular  cylinder,  on  the  other  hand,  js  the 
great  conducting  region,  as  well  as  one  that  gives  rigidity 
to  the  stem. 

If  the  vascular  cylinder  be  examined  closely,  it  will  be 
seen  that  it  is  broken  up  into  segments  by  plates  of  cells 
that  traverse  it  from  the  pith  to  the  cortex  (Fig.  204),  these 
radiating  plates  of  cells  being  the  pith  rays.  The  cylinder 
is  thus  made  up  of  a  number  of  segments  which  are  called 
vascular  bundles.  The  peculiarity  of  the  structure  of  the 
stem  in  Gymnosperms  and  Dicotyledons,  therefore,  can  be 
described  as  the  arrangement  of  the  vascular  bundles  so  as 
to  form  a  hollow  cylinder.  In  woody  stems  the  bundles  are 
very  close  together  in  the  cylinder,  forming  a  compact 
cylinder  with  narrow  pith  rays  (Fig.  204) ;  but  in  the  stems 
of  herbs  the  bundles  are  well  separated,  leaving  broad  pith 
rays  (Fig.  205). 

If  the  cross-section  of  an  individual  vascular  bundle  be 
examined  under  the  microscope,  two  regions  will  be  recognized 
(Fig.  206),  the  inner  omk,  toward  the  pith,  being  the  wood 
(xylem),  and  the  outer  one  being  the  bast  (phloem).  A  vas- 
cular bundle,  therefore,  is  made  up  of  xylem  and  phloem, 
which  differ  from  one  another  in  the  work  of  conduction, 
the  xylem  chiefly  conducting  the  water  that  enters  the  plants 
by  the  roots  and  is  passing  to  the  leaves,  and  the  phloem 
chiefly  conducting  prepared  food. 

The  cells  of  the  xylem  that  conduct  water  are  called 
tracheary  vessels.  They  are  more  or  less  elongated,  and  have 
very  thick  walls,  upon  which  there  appear  markings  of 
various  kinds  (Fig.  207).  These  markings  may  be  seen  in 
a  longitudinal  section  through  the  wood.  Some  of  the 
vessels  are  marked  by  a  spiral  band  that  extends  from  end 
to  end,  and  are  called  spiral  vessels  (Fig.  207,  A) ;  others 

^^Ctxt-tXo 

u---4  r 

-v 


238 


ELEMENTARY   STUDIES   IN   BOTANY 


show  a  series  of  thickened  rings,  and  are  called  annular 
vessels  (Fig.  207,  B) ;  while  others,  and  among  them  the 
largest,  have  numerous  thin  spots  in  their  walls  which  look 
like  dots  of  various  sizes,  and  these  are  the  doited  or  pitted 
vessels,  often  called  dotted  ducts  (Fig.  207,  C).  These  pitted 
vessels  are  often  very  large,  their  openings  being  visible  to 
the  naked  eye  in  the  cross-section  of  oak  wood. 


FIG.  207.  —  Vessels:  A,  spiral  vessels;  B,  annular  vessels;  C,  pitted  vessel  ("dotted 
duct ") ;  D,  sieve  vessel ;  E,  a  sieve-plate.  —  A  and  B  after  BONNIER  and  SABLON, 
C  after  DEBARY,  and  D  after  STRASBURGER. 

The  cells  of  the  bastjthat  conduct  prepared  food  are  called 
sieve  vessels,  TSecause  in  their  walls,  usually  the  end  walls, 
there  appear  areas  full  of  perforations,  like  the  lid  of  a  pepper- 
box, these  areas  being  called  sieve-plates  (Fig.  207,  D  and  E). 

A  prominent  feature  of  such  stems  is  that  they  can  in- 
crease in  diameter.  If  the  stem  lasts  only  one  growing 
season,  that  is,  if  it  is  an  annual,  there  is  no  increase  in  di- 
ameter ;  but  if  it  lasts  through  several  seasons,  that  is,  if  it 
is  a  perennial,  it  increases  in  diameter  from  year  to  year. 
Naturally,  annual  stems  belong  to  herbs  and  perennial 


STEMS 


239 


m 


w 


stems  to  shrubs  and  trees.  Taking  the  trees  as  an  illustra- 
tion, the  increase  in  diameter  occurs  as  follows.  Between 
the  xylem  and  the  phloem  of  each  bundle  is  a  layer  of  very 
active  cells  called  the  cambium  (Fig.  206),  which  soon  extends 
across  the  intervening  pith  rays  (Fig.  205),  and  so  forms 
a  complete  cylinder  of  cambium.  This  cambium  has  the 
power  of  adding  new  xylem  cells  to  the  outer  surface  of  the 
xylem,  and  new  phloem 
cells  to  the  inner  surface  of 
the  phloem,  as  well  as  of 
adding  to  the  pith  rays 
where  it  traverses  them. 
In  this  way  a  new  layer  of 
wood  is  laid  down  on  the 
outside  of  the  old  wood; 
and  usually  these  layers, 
added  year  after  year,  are 
so  distinct  that  a  section 
of  wood  shows  a  series  of 
concentric  rings  (Fig.  208). 
Ordinarily  one  such  layer 
is  added  each  year,  and 
hence  the  layers  are  called 
annual  rings.  The  age  of  a 
tree  is  usually  estimated  by 

counting  these  rings,  but  occasionally  more  than  one  ring  may 
be  added  during  a  single  year.  The  new  layers  added  to  the 
phloem  are  not  persistent ;  but  the  xylem  accumulates  year 
after  year,  until  in  an  ordinary  tree  the  stem  is  a  great  mass 
of  xylem  covered  with  thin  layers  of  phloem  and  cortex. 
It  is  this  mass  of  wood  that  supplies  our  lumber. 

This  annual  increase  in  diameter  enables  the  tree  to  put 
out  an  increased  number  of  branches,  and  hence  leaves,  each 
succeeding  year,  so  that  its  capacity  for  leaf-work  becomes 
greater  year  after  year.  A  reason  for  this  is  that  since 


FIG.  208.  —  Cross-section  of  a  branch  of  box- 
elder  three  years  old,  showing  three 
annual  rings  in  the  vascular  cylinder ;  the 
radiating  lines  (m)  that  cross  the  vascular 
cylinder  (w)  represent  the  pith  rays,  the 
principal  ones  extending  from  pith  to 
cortex  (c). 


240  ELEMENTARY   STUDIES   IN   BOTANY 

xylem  is  conducting  water  to  the  leaves,  the  new  layers 
enable  it  to  conduct  more  water,  and  more  leaves  can  be 
^  supplied. 

When  a  stem  increases  in  diameter,  it  is  very  seldom  that 
the  epidermis  grows  in  proportion.  Hence  it  is  usually 
sloughed  off  and  a  new  protective  covering  is  developed  by 
the  cortex.  Either  the  outermost  layer  of  the  cortex  or 
some  deeper  one  becomes  a  cambium,  which  means  that  it  is 
able  to  form  new  cells.  This  cambium  is  called  the  cork 
cambium,  since  it  forms  at  its  outer  surface  layer  after  layer 
of  cork  cells,  which  are  peculiarly  resistant  to  water.  If  the 
cork  cambium  is  formed  deep  in  the  cortex,  all  the  cells 
outside  of  it  die,  since  they  are  cut  off  from  the  water  supply 
in  the  plant.  The  cork  cambium  is  often  renewed  year 
after  year,  and  two  prominent  kinds  of  bark  are  formed. 
In  some  cases  the  successive  cork  cambiums  form  zones 
completely  about  the  stem,  and  the  cork  is  then  deposited 
in  concentric  layers,  forming  the  ringed  bark.  Such  bark 
often  becomes  very  thick,  and  the  surface  becomes  seamed 
or  furrowed.  In  the  cork  oak,  for  example,  there  is  a  very 
great  accumulation  of  cork,  which  is  stripped  off  in  sheets, 
from  which  corks  of  commerce  are  made.  In  other  cases 
the  successive  cork  cambiums,  instead  of  passing  completely 
around  the  stem,  run  into  the  next  outer  one,  thus  cutting 
out  segments  which  presently  loosen  and  flake  off,  forming 
scaly  bark,  as  in  hickory,  apple,  etc. 

The  layers  of  cork  and  other  cells  that  may  lie  outside 
of  the  cork  cambium  form  the  outer  bark,  which  is  dead  and 
dry.  The  tissues  between  the  cork  cambium  and  the  cam- 
bium of  the  vascular  cylinder,  that  is,  more  or  less  of  the 
cortex  and  all  of  the  phloem,  form  the  inner  bark,  which 
contains  some  living  cells.  To  remove  the  outer  bark  does 
not  injure  a  tree;  but  removing  the  inner  bark  kills  it, 
because  it  interrupts  the  work  of  conduction  carried  on  by 
the  sieve  vessels.  In  the  process  known  as  girdling,  not  only 


STEMS  241 

is  the  bark  cut  through,  but  the  young  wood  is  cut  into. 

This  interferes  with  the  movement  of  water  up  the  stem  as 

well   as  with   conduction  by  the  sieve-vessels.     If  a  small 

portion  of  the  bark  is  removed,  the  incision  extending  only 

to  the  wood,  as  in  the  making  of  inscriptions  on  trees,  the 

wound  is  healed,  unless  too  large,  by  the  growth  of  tissue 

from  all  sides  until  it  is  closed  over.     In  this  new  tissue  a  cork 

cambium    is    developed, 

and  presently  there  may 

be  no  surface  indication 

of  the   wound.      But  if 

the     wound     has     gone 

deeper  and  entered   the 

wood,   the   record    of   it 

may  always  be  found  in 

the   wood   by   removing 

the  bark.     In  this  way 

old     inscriptions      have 

often  been  uncovered. 

The  well-known  opera- 
tion of  grafting  depends 
upon  the  ability  of  plants 
to  heal  wounds.  The 
plant  upon  which  the 

.  .  FIG.   209.  —  Cleft-grafting,    showing   scions   in 

Operation     IS      performed  place  (A)  and  the  wound  sealed  with  clay 

is   called   the   stock,  and 

the  twig  grafted  into  it  the  scion.  An  ordinary  method,  called 
cleft-grafting,  is  to  cut  off  the  stem  or  a  branch  of  the  stock, 
split  the  stump,  insert  into  the  cleft  the  wedge-shaped  end 
of  the  scion,  and  seal  up  the  wound  with  wax  or  clay  (Fig. 
209).  The  cambiums  of  the  stock  and  the  scion  must  be 
put  into  contact  at  some  point;  and  hence  it  is  usual  to 
insert  a  scion  in  each  side  of  the  cleft,  since  the  cambium  of 
the  stock  is  comparatively  near  the  surface.  The  cambiums 
of  stock  and  scion  unite,  the  wound  heals,  and  the  scion 


242 


ELEMENTARY    STUDIES   IN   BOTANY 


becomes  as  closely  related  to  the  activities  of  the  stock  plant 
as  are  the  ordinary  branches.  The  scions  are  usually  cut 
in  the  fall,  after  the  leaves  have  fallen,  are  kept  through 
the  winter  in  moist  soil  or  sand,  and  the  grafting  is  done 
in  the  spring.  A  number  of  important  things  are  secured 
by  grafting,  but  chief  among  them  is  the  propagation  of 
useful  varieties  with  certainty  and  with  a  great  saving  of 
time,  as  compared  with  their  propagation  from  the  seed. 

In  Monocotyledons  the  vascularJpundles  of  the  stem  are 
not  arranged  so  as  to  form  a(ftyillow  cylinder,  but  are 
more  or  less  irregularly  scattered,  as  may  be  seen  in  a 

cross-section  of  a  corn-stalk  (Fig. 
210).  As  a  consequence,  there 
is  no  inclosing  of  a  definite  pith, 
nor  is  there  any  distinctly  bounded 
cortex.  In  the  bundles  there  is  no 
cambium,  and  therefore  new  w 
and  bast  cannot  be  added  to  the 
old,  so  that  in  the  trees  there  is 
no  annual  increase  in  diameter; 
and  this  means  that  there  is  no 


!7'1? 


FK,  210.- cross  andTongitudi-    branching  and  no  increased  foliage 
nai  sections  of  a  cornstalk,    from  year  to  year.      A  palm  well 

showing    the    scattered    vas-      ...  ,.       ,      ,   .  .    ,       . 

cuiar  bundles.  illustrates  this  habit,  with  its  co- 

lumnar, unbranching  trunk,  and  its 

crown  of  leaves,  which  continue  about  the  same  in  number 
each  year. 

134.  Ascent  of  sap.  —  The  water  entering  the  plant  by 
the  roots  and  moving  upward  through  the  stem  is  usually 
called  sap.  It  is  not  pure  water,  but  contains  certain  soil 
substances  dissolved  in  it.  In  low  plants,  as  most  annuals, 
the  ascent  of  sap  requires  no  special  explanation;  but  in 
plants  such  as  trees,  in  which  the  crown  of  leaves  is  many 
feet  above  the  soil,  the  case  is  very  .different.  Several  ex- 
planations of  the  ascent  of  sap  in  trees  have  been  suggested, 


STEMS  243 

and  all  of  the  older  ones  have  been  disproved,  so  that  we  are 
still  waiting  for  an  explanation  that  will  stand  the  test  of 
experiment. 

That  the  path  of  ascent  ijrthrough  the  vessels  of  the  xylem, 
and  not  through  cortex  or  phloem  or  pith,  may  be  demon- 
strated by  a  simple  experiment.  A  stem  of  corn  or  sun- 
flower or  balsam  is  cut  off  and  placed  in  water  for  an  hour. 
Then  it  is  transferred  to  a  vessel  containing  water  stained 
with  cheap  red  ink  (a  solution  of  eosin),  and  exposed  to 
diffuse  light.  A  few  hours  later,  sections  of  the  stem  will 
show  the  xylem  vessels  stained  red,  the  ascending  water 
having  stained  its  path.  Of  course  the  stain  may  spread 
somewhat  into  adjacent  cells.  It  must  be  remembered 
that  the  xylem  vessels  are  not  living  cells  when  they  become 
the  best  water-carriers,  so  that  the  movement  of  water 
through  them  is  not  like  the  movement  of  water  from  one 
living  cell  to  another.  When  the  great  distance  to  be  trav- 
ersed by  water  in  a  tall  tree  is  considered,  this  movement 
of  water  through  a  system  of  dead  cells  is  a  very  important 
fact  to  explain. 

In  most  trees,  as  the  mass  of  wood  increases  in  diameter, 
the  ascending  sap  abandons  the  inner  (older)  wood  and  moves 
only  through  the  newer  wood.  This  results  in  a  different 
appearance  of  the  two  regions,  the  old  central  wood,  aban- 
doned by  the  sap,  becoming  darker  and  often  characteristi- 
cally colored  (heart  wood),  and  the  younger  outer  wood, 
used  by  the  sap,  being  lighter  colored  (sap  wood).  Trees 
vary  greatly  in  the  relative  thickness  of  the  sap  wood ;  for 
example,  in  the  beech  it  is  a  thick  zone,  while  in  the  oak  it  is 
a  narrow  one.  In  successful  girdling  this  must  be  taken  into 
account,  since  an  incision  which  would  cut  off  the  water 
supply  of  an  oak  sufficiently  to  kill  it  would  not  kill  a  beech. 

The  rate  of  movement  of  the  ascending  sap  of  course  varies 
with  different  plants  and  different  conditions.  In  the  pump- 
kin-vine, in  which  the  movement  is  very  rapid,  it  has  been 


244 


ELEMENTARY   STUDIES   IN   BOTANY 


found  to  reach  about  twenty  feet  an  hour.     It  is  estimated 

that  in  ordinary  broad-leaved  trees  the  rate  is  probably 

three  to  six  feet  an  hour. 

If  certain  stems  are  cut  off  near  the  ground,  it  is  observed 

that  after  a  short  time  the  sap  begins  to  ooze  out,  a  phenome- 
non that  is  often  called  " bleeding." 
In  some  woody  plants,  as  grape-vines 
and  birches,  the  sap  flows  out  with 
considerable  force,  indicating  some 
pressure  below,  which  is  called  root- 
pressure.  While  root-pressure  may 
force  the  sap  into  the  stem,  it  is 
entirely  inadequate  to  force  it  to  the 
top  of  a  tree. 

The  so-called  maple  sap  obtained 
from  the  sugar  maple  is  an  interesting 
illustration  of  the  use  of  sap  that  ac- 
cumulates in  a  woody  stem  in  the 
spring.  At  that  time  the  water  has 
no  opportunity  to  escape  through  leaf 
transpiration ;  so  the  wood  becomes 
gorged  with  sap,  which  can  be  drawn 
off  by  boring  into  the  wood  and  in- 
serting spiles.  The  characteristic  sugar 
has  been  obtained  by  the  sap  from 

FIG.    211.  —  Scarlet    runner       ...  .  i  i        • 

bean  marked  with  a  scale      f  OOCl    stored    in    the    stem,     notably    111 
of   five   millimeter   inter-       ,1  i  i  j 

the  older  wood. 


135.   Growth   in   length.  —  Growth 


vals  and  photographed 
after  forty-eight  hours ; 
the  lines  closest  together 

show  the  original  spac-    in    length    begins    at   the  tip  of  the 
stem  by  the  formation  of  new  cells, 

which  are  organized  into  the  alternating  nodes  and  internodes. 
When  these  regions  are  first  formed,  the  internodes  are  very 
short,  and  their  subsequent  elongation,  separating  the  nodes,  is 
the  chief  cause  of  the  lengthening  of  the  stem.  Internodes 
are  able  to  elongate  for  only  a  certain  time,  so  that  the 


STEMS 


245 


elongating  portion  of  a  stem  does  not  often  extend  more 
than  ten  to  twenty  inches.  Seedlings  such  as  those  of  the 
bean  should  be  cultivated,  and  the  region  of  growth,  the 
region  of  greatest  growth,  and  the  rate  of  growth  determined. 
To  do  this,  each  internode  is  marked  with  equally  spaced 
lines  in  India  ink,  and  measuring  these  spaces  at  intervals. 


FIG.  212.  —  Axillary  (and  therefore  branch)  thorns:    A,  honey  locust;    B,  hawthorn. 


of  one  or  two  days  will  determine  the  facts  referred  to  above 
(Fig.  211). 

136.  Subterranean  stems.  —  Since  stems  (or  branches) 
usually  bear  foliage  leaves,  any  stem  which  does  not  is 
spoken  of  as  "  modified."  For  example,  branches  that 
become  thorns  (Fig.  212),  tendrils  (Fig.  213),  leaf-like 
structures  (Fig.  193),  etc.,  are  thought  of  as  stems  diverted 
from  their  ordinary  use. 
17 


246  ELEMENTARY   STUDIES   IN   BOTANY 

The  most  common  "  modifications  "  of  the  stem  are  those 
which  arise  when  it  is  an  underground  structure,  and  thickened 
.subterranean  stems  are  not  only  common  among  plants, 


FIG.  213.  —  Plants  of  passion-flower  showing  axillary  (and  therefore  branch)  tendrils. 


but  also  are  often  of  great  use  to  man.  Since  the  stem  is 
primarily  a  leaf-bearing  structure,  it  continues  to  bear 
leaves  when  underground,  but  often  these  leaves  are  either 
reduced  in  size  so  as  to  be  mere  rudiments,  or  are  used  in 


FIG.  214.  —  Rootstock  of  a  fern  bearing  young  leaves. 


FIG.  215.  —  Rootstock  of  a  rush  (Juncus),  showing  how  it  advances  beneath  the  ground 
and  sends  up  a  succession  of  branches ;  the  breaking  up  of  such  a  rootstock  only 
results  in  separate  individuals. 


247 


248  ELEMENTARY    STUDIES   IN   BOTANY 

some  other  way  than  as  foliage.  A  stem  and  its  leaves  taken 
together  constitute  the  shoot  (as  contrasted  with  the  root), 
and  since  both  must  be  considered  in  connection  with  the 
subterranean  habit,  the  shoot,  rather  than  the  stem  alone, 
will  be  discussed.  A  subterranean  shoot  may  be  distin- 
guished from  a  root  not  only  by  the  leaves  (or  structures 
representing  leaves)  it  bears,  but  also  by  its  internal  struct- 
ure, which  is  very  different  from  that  of  a  root,  as  will  appear 
in  the  next  chapter.  In  general,  the  subterranean  shoot 


FIG.  216.  —  Rootstock  of  Solomon's  seal,  showing  terminal  bud,  the  base  of  this  year's 
aerial  branch,  and  scars  of  the  branches  of  three  preceding  years.  —  After  GRAY. 

is  used  for  food  storage,  and  the  three  following  kinds  are 
the  most  common. 

(1)  Rootstock.  —  This  is  probably  the  most  common  form 
of  subterranean  stem  (also  called  a  rhizome).  It  is  usually 
horizontal,  more  or  less  elongated,  and  usually  much 
thickened  for  food  storage  (Fig.  214).  It  advances  through 
the  soil  year  after  year,  often  branching,  sending  out  roots 
beneath  and  leaf-bearing  branches  into  the  air.  As  it  con- 
tinues to  grow  at  the  apex,  it  gradually  dies  behind,  thus 
isolating  branches  in  the  case  of  branching  rootstocks.  It 
is  a  very  efficient  method  for  the  spreading  of  plants  and  is 
extensively  used  by  grasses  in  covering  areas  and  forming 
turf.  The  persistent  continuance  of  some  weeds,  especially 
certain  grasses  and  sedges,  that  infest  lawns  and  meadows, 
is  due  to  this  habit  (Fig.  215).  It  is  impossible  to  remove 
from  the  soil  all  of  the  indefinitely  branching  rootstocks, 


STEMS  249 

and  any  nodes  that  remain  are  able  to  send  up  fresh  crops 
of  aerial  branches.  In  many  cases  only  a  single  aerial  branch 
is  sent  up  each  year,  as  in  wild  ginger,  Solomon's  seal  (Fig. 
216),  iris,  bloodroot,  etc. ;  in  others,  leaves  and  flowers 
may  be  sent  up  separately  by  the  rootstock.  In  the  common 
ferns,  the  so-called  fronds  are  simply  large  leaves  developed 
directly  by  the  rootstock  (Fig.  214).  Perhaps  even  more 
familiar  is  the  extensive  rootstock  system  of  the  water- 
lilies,  from  which  arise  the  leaves  with  large  floating  blades 
(pads).  It  is  evident  that  a  rootstock  does  not  necessarily 
bear  only  scale  leaves,  but  it  may  develop  also  leaves  that 


FIG.  217.  —  Potato  tuber,  showing  "eyes"  (scale  leaves  with  their  axillary  buds). 

become  aerial,  and  in  that  case  they  are  usually  large.  In 
plants  possessing  rootstocks,  the  subterranean  stems  are 
perennial,  while  the  aerial  parts  may  be  annual. 

(2)  Tuber.  —  In  some  plants  the  ends  of  underground 
stems  or  branches  become  very  much  enlarged  in  connection 
with  food  storage.  These  enlargements  are  called  tubers, 
the  best-known  illustration  being  the  common  potato  (Fig. 
217).  That  it  is  a  stem  structure  is  evident  from  the  fact 
that  it  bears  very  much  reduced  leaves,  in  the  axils  of  which 
are  buds,  the  so-called  "  eyes."  Abnormally  developed 
potatoes  often  show  the  shoot  character  of  the  tuber  very 
plainly,  and  in  the  case  of  potatoes  sprouting  it  is  evident 
that  the  eyes  have  developed  into  branches.  In  planting 
potatoes,  as  has  been  said,  advantage  is  taken  of  the  fact 


250 


ELEMENTARY   STUDIES   IN   BOTANY 


that  any  node  placed  in  proper  conditions  may  strike  root 
and  put  out  a  branch.  Heaping  up  the  soil  ("  hilling  ") 
about  the  base  of  the  potato  plant  induces  the  formation 
of  more  of  the  subterranean  tuber-bearing  branches.  In 
the  tuber  called  Jerusalem  artichoke,  which  is  developed  by 
the  subterranean  stems  of  a  kind  of  sunflower,  the  nodes 
of  the  stem  and  the  buds  of  branches  are  more  conspicuous 
than  in  the  potato.  Fleshy  roots,  such  as 
those  of  the  sweet  potato,  should  not  be 
confused  with  tubers. 

(3)  Bulb.  —  In  some  plants  the  main 
stem  is  very  short  and  is  covered  by 
numerous  thickened,  overlapping  leaves 
or  leaf  bases  (usually  called  scales),  the 
whole  structure  being  a  bulb.  Bulbs  such 
as  those  of  the  lily,  hyacinth,  tulip,  and 
onion  are  very  familiar.  In  this  case 
the  food  storage  is  chiefly  in  the  scales. 
Scaly  bulbs  are  those  in  which  the  scales 
overlap,  but  are  not  broad  enough  to 
inwrap  those  within,  as  the  lily  bulb  (Fig. 
218) ;  coated  bulbs  are  those  in  which  the 
broad  scales  completely  inwrap  those  within,  as  the  bulbs 
of  onions  and  tulips.  Small  bulbs,  called  bulblets,  are 
borne  by  some  plants  on  parts  above  ground ;  as,  for  ex- 
ample, the  bulblets  that  appear  in  the  axils  of  the  leaves 
of  the  tiger-lily  and  those  that  replace  flower-buds  in  the 
common  onion  ("  onion  sets  ")•  These  bulblets,  when  planted, 
have  the  power  of  producing  new  plants,  as  do  the  sub- 
terranean bulbs. 

These  subterranean  shoots,  with  their  storage  of  reserve 
food,  enable  plants  to  put  out  their  aerial  parts  with  re- 
markable promptness  and  develop  them  with  great  rapidity. 
As  an  illustration  of  a  situation  in  which  this  ability  is  of 
great  advantage  to  plants,  the  vernal  habit  may  be  mentioned. 


FIG.  218. —  The   scaly 
bulb  of  a  lily. 


STEMS  251 

It  is  a  matter  of  common  observation  that  the  rich  display 
of  spring  flowers  occurs  in  forests  and  wooded  glens  before 
the  trees  come  into  full  foliage.  The  working  season  of 
these  spring  plants  is  between  the  beginning  of  the  growing 
season  and  the  full  forest  foliage,  and  the  subterranean 
shoots  enable  them  to  send  up  their  aerial  parts  with  great 
rapidity.  After  the  forest  leaves  are  fully  developed,  the 
available  light  for  work  beneath  the  forest  crown  diminishes, 
the  spring  flowers  disappear,  and  the  short  period  of  activity 
does  not  return  until  the  next  season. 

Another  situation  in  which  speed  of  development  is  of 
great  advantage  to  the  plant  is  in  regions  in  which  there  is 
a  short  rainy  season  and  a  long  dry  season.  In  such  regions 
the  annuals  spring  up  with  remarkable  rapidity,  and  in  most 
cases  this  is  made  possible  by  food  storage  in  underground 
stems. 

137.  Summary.  —  The  most  important  fact  about  a  stem 
is  that  it  produces  and  displays  leaves.  The  nodes  not  only 
produce  leaves,  but  also  branches,  and  if  the  conditions  favor 
it,  they  can  produce  roots  also ;  therefore  it  is  possible  to 
reproduce  a  whole  plant  from  a  node,  a  fact  that  is  taken 
advantage  of  in  the  propagation  of  many  plants. 

The  vascular  system  forms  a  hollow  cylinder  in  the  stems 
of  Gymnosperms  and  Dicotyledons,  a  cylinder  that  incloses 
pith  and  is  surrounded  by  cortex.  The  two  regions  of  the 
vascular  cylinder  are  xylem  and  phloem,  and  in  Gymno- 
sperms and  Dicotyledons  the  xylem  is  next  to  the  pith  and 
the  phloem  next  to  the  cortex.  A  notable  feature  of  such 
a  stem  is  the  presence  of  the  cambium  between  the  phloem 
and  xylem,  which  adds  new  elements  to  each  region.  The 
additions  to  the  xylem  in  the  case  of  perennial  stems  (not- 
ably trees)  result  in  an  annual  increase  of  wood,  which 
usually  appears  as  annual  rings.  This  yearly  increase  in 
the  capacity  for  carrying  water  is  associated  with  the  pos- 
sibility of  an  annual  increase  of  branches  and  leaves. 


252  ELEMENTARY   STUDIES   IN   BOTANY 

When  a  stem  increases  in  diameter  by  the  annual  increase 
of  xylem,  the  epidermis  usually  does  not  keep  pace  with  it 
and  is  sloughed  off.  In  any  event,  a  cambium  appears  in 
the  cortex  and  produces  cork  cells  that  form  a  most  efficient 
protective  jacket  and  that  give  character  to  what  is  called 
"bark." 

Subterranean  stems  can  be  distinguished  from  roots  by 
the  presence  of  nodes  bearing  leaves,  or  at  least  rudiments 
of  leaves.  The  subterranean  habit  is  often  associated  with 
food  storage,  the  significance  of  which  is  that  it  enables  the 
plant  to  develop  its  aerial  parts  with  great  rapidity,  and 
thus  to  make  the  most  of  a  short  season.  This  is  one  of 
the  chief  reasons  why  rootstocks,  tubers,  and  bulbs  are  used 
in  the  propagation  of  cultivated  plants,  new  plants  being 
obtained  much  more  speedily  than  by  means  of  seeds. 


CHAPTER  XIII 
ROOTS 

138.  General  character.  —  Roots  are  thought  of  as  struct- 
ures related  to  the  soil.  This  is  true  of  most  roots,  and  it 
is  certainly  true  of  the  roots  of  those  plants  we  cultivate. 


BBHHBBB 

A  B 

FIG.  219.  —  Roots :   A,  dandelion  with  tap-root ;   B,  grass  with  cluster  of  fibrous  roots. 

However,  there  are  also  water  roots  and  air  roots,  so  that  the 
soil-relation  is  not  the  only  one  for  roots,  but  this  presenta- 
tion will  be  restricted  chiefly  to  soil  roots. 

253 


254 


ELEMENTARY    STUDIES   IN   BOTANY 


Roots  differ  from  subterranean  stems  even  in  external 
appearance,  since  they  do  not  bear  leaves  or  scales  and  do 
not  have  nodes.  It  should  be  remembered  that  roots  are 
produced  not  only  by  the  hypocot}d  (§  113,  p.  180),  but  also 
by  the  nodes  of  stems.  It  is  convenient  to  distinguish  these 
two  origins  by  calling  the  roots  developed  by  the  embryo 
primary  roots,  and  those  not  developed  by  the  embryo 

secondary  roots.  It  has  been  ob- 
served (§  136,  p.  248)  how  sub- 
terranean stems,  prostrate  stems, 
and  even  erect  stems  "  strike 
root  "  from  the  nodes,  and  such 


FIG.  220.  —  Fleshy  roots;    A,  radish  with  fleshy  tap-root;    B,  dahlia  with  cluster  of 

fleshy  roots. 

secondary  roots  are  the  only  roots  of  many  plants.  For 
example,  when  a  new  plant  is  developed  by  "  layering  "  a 
raspberry  (§  131,  p.  232),  or  planting  a  "  slip  "  or  "  cutting  " 
from  a  grape-vine,  or  planting  slices  of  a  potato  tuber, 
secondary  roots  are  the  only  kind  possible,  for  the  new 
plants  are  not  produced  by  seeds. 

The  primary  root  developed  by  the  hypocotyl  may  con- 
tinue as  a  conspicuous,  vertically  descending  axis  that  gives 
off  small  branches  (Fig.  219,  A) ;  or  it  may  break  up  at  once 


ROOTS 


255 


into  a  cluster  of  branches  (Fig.  219,  B).  In  the  former  case, 
the  plant  is  said  to  have  a  tap-root;  and  in  the  latter  case, 
when,  as  in  grasses,  the  clustered  branches  are  slender,  the 
plant  is  said  to  have 
fibrous  roots.  In  both 
cases  the  root  may  be- 
come enlarged  in  con- 
nection with  food  stor- 
age, and  many  of  our 
common  vegetables  are 
such  thickened  roots. 
For  example,  radish 
(Fig.  220,  A),  turnip, 
and  parsnip  are  thick- 
ened tap-roots ;  while 
sweet  potatoes  are  the 
thickened  branches  of  a 
cluster  of  roots,  as  in 
the  dahlia  (Fig.  220, 
B).  It  is  evident  that 
thickened  roots,  just  as 
thickened  underground 
stems  (§  136,  p.  250), 
enable  the  plant  to  de- 
velop its  aerial  parts 
much  more  quickly  than 
by  the  method  of  seed- 
germination. 

139.  Root-cap.— The 
growing  tip  of  each  root 
and  rootlet  is  protected 
by  a  cap  of  cells  called  the  root-cap  (Fig.  221,  c).  This 
root-cap  consists  of  several  layers  of  cells,  the  outer  ones 
gradually  dying  or  being  worn  away  as  the  tip  of  the  root 
pushes  through  the  soil,  and  being  replaced  by  new  layers 


FIG.  221.  —  Longitudinal  section  through  root- 
tip  of  spiderwort,  showing  central  vascular 
cylinder  (pi),  cortex  (p),  epidermis  (e),  and 
root-cap  (c). 


256 


ELEMENTARY   STUDIES   IN   BOTANY 


which  are  continually  forming  beneath.  In  some  plants  the 
root-cap  is  very  easily  seen  as  a  conical  thickening  at  the  tip 
of  the  root ;  in  others  it  can  be  demonstrated  only  by  examin- 
ing under  the  microscope  longitudinal  sections  through  the 
root-tip.  The  presence  of  such  a  protective  cap  in  the  root 
is  in  strong  contrast  with  the  stem,  whose  growing  tips  are 
protected  by  overlapping  leaves. 

140.  Root-hairs.  —  A  short  distance  behind  the  root-cap 
the  surface  of  the  root  becomes  covered  by  a  more  or  less 

dense  growth  of  hairs,  known  as 
root-hairs  (Fig.  222).  These 
hairs  are  outgrowths,  sometimes 
very  long  ones,  from  the  epi- 
dermal cells,  a  single  cell'  pro- 
ducing a  single  root-hair.  In 
fact,  the  root-hair  is  only  an 
extended  part  of  the  epidermal 
cell.  The  root  receives  water 
and  materials  dissolved  in  it 
from  the  soil,  and  the  root- 
hairs  enormously  increase  the 
receiving  surface.  Root-hairs 
do  not  last  very  long;  but 
new  hairs  are  being  put  out 
by  the  elongating  root  as  the 
old  ones  behind  die,  so  that 

there  is  always  a  zone  of  active  root-hairs  near  the  tip,  but 

none  on  the  older  parts  of  the  root. 

141.  Internal  structure.  —  A  cross-section  of  a  young  root 
shows  two  prominent  regions  (Fig.  223).     In  the  centre  is  a 
solid  vascular  cylinder,  often  called  the  central  axis.     It  will 
be  remembered  that  in  the  stems  of  Dicotyledons  and  Gym- 
nosperms  (§  133,  p.  236)  the  vascular  cylinder  is  hollow,  in- 
closing pith.     Investing  the  solid  vascular  cylinder  of  the 
root  is  the  cortex,  which  often  can  be  stripped  from  the 


FIG.  222.  —  Root  tips  of  corn,  showing 
root-hairs  and  their  position  in 
reference  to  the  growing  tip. 


ROOTS 


257 


central  axis  like  a  spongy  bark.  If  the  section  has  passed 
through  the  zone  of  root-hairs,  they  can  be  seen  coming 
from  the  epidermal  cells.  A  longitudinal  section  of  a  root- 
tip,  in  which  these  regions  are  very  young,  is  shown  in 
Fig.  221. 

The  xylem  and  phloem  of  the  vascular  cylinder  of  the  root 
do  not  hold  the  same  relation  to  each  other  as  in  the  stem 
(§  133,  p.  237).  The  vascular  cylinder,  instead  of  being 
made  up  of  vascular  bundles  with 
xylem  toward  the  centre  and 
phloem  toward  the  outside,  as 
in  the  stems  of  Seed-plants,  is 
made  up  of  xylem  and  phloem 
strands  alternating  with  each 
other  around  the  centre  (Fig. 
223).  The  xylem  strands  radiate 
from  the  centre  like  the  spokes 
of  a  wheel,  and  the  phloem  strands 
are  between  these  spokes  near 
their  outer  ends.  This  arrange- 
ment of  xylem  and  phloem  is 
peculiar  to  roots. 

When  roots  increase  in  diam- 
eter, a  cambium  soon  begins  to  form  new  xylem  and 
phloem,  as  in  the  stems  that  increase  in  diameter  (§  133, 
p.  239).  The  new  xylem,  however,  is  not  formed  in  con- 
nection with  the  old  wood,  but  just  within  the  phloem, 
that  is,  farther  in  between  the  "  spokes  "  of  old  wood, 
resulting  in  bundles  like  those  of  the  stem  (Fig.  224).  In 
this  way  a  thickened  vascular  cylinder  is  formed,  like  that 
of  stems  that  increase  in  diameter ;  and  presently  the  cross- 
section  of  the  root  resembles  that  of  the  stem.  It  is  evident 
(Fig.  224)  that  the  principal  pith  rays  that  traverse  the  wood 
zone  formed  by  the  cambium  (secondary  wood)  extend  in- 
ward to  the  original  radiating  strands  of  wood  (primary 


FIG.  223.  —  Cross-section  of  a  young 
root,  showing  the  solid  vascular 
cylinder,  the  extensive  cortex, 
and  the  epidermis  ;  observe  that 
the  xylem  extends  from  the  cen- 
tre in  four  strands,  between 
which  the  phloem  strands  are 
seen. 


258 


ELEMENTARY   STUDIES   IN   BOTANY 


wood)  that  alternate  with  the  original  strands  of  phloem. 
The  vascular  bundles  of  the  root  connect  with  those  of  the 
stem,  and  these  in  turn  with  those  of  the  leaves,  so  that 
throughout  the  whole  plant  there  is  a  continuous  vascular 
system. 

The  origin  of  the  branches  of  roots  is  very  different  from 
that  of  stems.  In  a  stem  the  branch  begins  at  the  outer 
part  of  the  cortex,  but  in  the  root  it  begins  at  the  surface  of 


FIG.  224.  —  Diagram  to  show  how  roots  increase  in  diameter :  A  represents  cross-sec- 
tion of  a  young  root  in  which  four  phluem  strands  (p)  alternate  with  four  xylem 
strands  (x)  ;  B  represents  an  older  root  in  which  there  is  a  continuous  zone  of 
cambium  (c)  that  is  forming  on  the  outside  new  phloem  (np)  in  contact  with  the  old 
(p),  and  on  the  inside  new  xylem  (nx)  alternating  with  the  old  (x). 

the  vascular  cylinder  and  breaks  through  the  cortex  (Fig. 
225).  If  the  cortex  of  a  root  be  stripped  off,  the  branches 
will  be  found  attached  to  the  central  axis,  and  the  perfora- 
tions made  by  the  branches  through  the  cortex  can  be  seen. 
142.  Growth  in  length.  —  The  elongating  region  of  the 
root  is  much  more  restricted  than  that  of  the  stem.  It  was 
stated  (§  135,  p.  244)  that  the  elongating  region  of  a  stem 
may  extend  ten  or  twenty  inches  from  the  tip,  or  even  more  ; 
but  the  elongating  region  of  a  root  is  hardly  ever  more  than 
two-fifths  of  an  inch,  and  often  not  more  than  half  of  that/ 
The  region  of  elongation  and  of  greatest  elongation  should 


ROOTS 


259 


be  determined  by  using  such  seedlings  as  those  of  peas, 
beans,  and  corn.  When  the  young  roots  have  become  a  half 
to  one  inch  long,  mark  as  delicately  as  possible  in  India  ink 
with  a  soft,  camel's  hair  brush  a  series  of  equally  spaced 
lines,  beginning  at  the  tip.  Observations  at  the  end  of 
twenty-four  to  forty-eight  hours  will  reveal  the  region  of 
elongation  and  of  greatest  elongation 
(Fig.  226). 

143.  The  soil.  —  The  soil  is  too 
commonly  thought  of  as  merely  an  ac- 
cumulation of  "  dirt,"  from  which 
plants  can  obtain  "  food."  It  has 
been  pointed  out  in  preceding  chapters 
that  ordinary  plants  do  not  obtain 
food  from  the  soil,  but  that  they  do 
obtain  certain  materials  used  in  food- 
manufacture.  It  now  remains  to  con- 
sider whether  the  soil  is  merely  "dirt." 

Soil  is  finely  divided  rock  (mineral) 
material,  which  in  "rich"  soil  is  mixed 
with  more  or  less  organic  material  de- 
rived from  the  broken-down  bodies  or 
waste  products  of  plants  and  animals. 
It  is  the  organic  material  that  makes 
soils  dark,  and  when  there  is  a  considerable  amount  of  this, 
as  in  the  upper  soil  of  forests,  the  soil  is  called  humus  (often 
"  vegetable  mould  "  or  "  leaf  mould  ").  Soil,  therefore,  is  a 
mixture  of  certain  mineral  (inorganic)  and  organic  materials. 
These  materials  must  include  certain  chemical  substances 
that  plants  need,  and  in  general  all  soils  contain  these  sub- 
stances. This  is  indicated  by  the  fact  that  almost  all  soils 
in  nature  are  covered  by  vegetation,  and  even  in  the  desert 
of  Sahara,  reputed  to  have  the  most  "  sterile  "  of  soils,  the 
breaking  through  to  the  surface  of  a  spring  of  water  results 
in  an  "  oasis  "  with  luxuriant  vegetation.  This  indicates 


FIG.  225.  —  Longitudinal 
section  of  root  of  ar- 
row-leaf, showing  the 
branches  starting  from 
the  vascular  cylinder  and 
penetrating  the  cortex. 


260  ELEMENTARY   STUDIES   IN    BOTANY 

that  the  chemical  composition  of  all  soils  is  appropriate  for 
plants,  and  that  the  differences  between  soils  is  not  so  much 
a  question  of  proper  or  improper  chemical  constitution  as  of 
something  else.  The  chemical  composition  of  soils  is  uni- 
formly appropriate  for  plants  in  the  same  general  sense  that 
the  air  is  uniformly  appropriate  for  them.  It  is  sometimes 
said  that  the  chemical  composition  of  soils  "  makes  no  dif- 
ference," but  this  does  not  mean  that  it  is  not  extremely 
important,  any  more  than  the  statement  that  the  air  "  makes 
no  difference  "  would  indicate  that  the  air  is  not  important. 

It  makes  no  difference  sim- 
ply because  it  is  always 
present. 

The  great  differences 
among  soils  have  to  do 
with  their  power  to  handle 
water,  and  this  is  a  physi- 
cal property  of  the  soil 
rather  than  a  question  of 
chemical  composition.  The 

FIG.    226.  —  Roots    of   scarlet   runner   bean        power    of    a    Soil   to   receive 
marked  with  lines  one  millimeter  apart  ,  . 

and  photographed  after  forty-eight  hours.        and    to    retain     Water    IS    a 

very  important  consider- 
ation in  connection  with  plants.  For  example,  it  is 
evident  that  the  receptive  power  of  sand  is  high,  but 
its  retentive  power  is  low;  while  in  the  case  of  clay  the 
reverse  is  true.  One  of  the  great  advantages  of  humus  is 
that  its  receptive  and  retentive  powers  are  better  balanced 
than  in  sand  and  clay.  It  is  easy  to  devise  a  series  of  experi- 
ments that  will  show  in  a  rough  way  the  comparative  recep- 
tive and  retentive  powers  of  these  three  types  of  soil.  It  has 
been  shown  also  that,  for  any  given  soil,  the  more  finely  the 
particles  are  divided  the  better  it  is  for  plants.  When  the  soil 
is  turned  up  with  plough  or  spade,  it  is  dried  by  the  air  and 
pulverized  and  so  put  in  better  physical  condition  for  hand- 


ROOTS  261 

ling  water.  It  is  evident  that  in  considering  the  relation  of 
soil  to  plants,  not  only  the  surface  soil  must  be  considered, 
but  also  the  soil  beneath  (subsoil).  For  example,  if  humus 
rests  on  sand,  the  water  will  drain  away  much  more  rapidly 
than  if  humus  rests  on  clay. 

It  is  necessary  to  understand  the  physical  structure  of  the 
soil  in  relation  to  water.  However  fine  the  particles  of  soil 
may  be,  they  never  fit  together  in  close  contact,  so  that  there 
are  open  spaces  everywhere  among  them.  Immediately 
after  a  soaking  rain  these  spaces  are  full  of  water,  but  if  the 
soil  is  one  that  drains  easily,  the  water  gradually  disappears 
from  the  spaces,  and  the  largeV  ones  are  occupied  by  air. 
In  addition  to  this  occasional  supply  of  water,  each  particle 
of  soil  is  invested  by  a  thin  film  of  water,  which  adheres  to 
it  closely,  and  which  never  entirely  disappears  even  in  the 
driest  soil.  It  is  the  water  of  the  adherent  films  that  enters 
the  roots,  and  not  the  "  free  water  "  that  may  occur  in  the 
spaces  between  the  soil  particles.  These  spaces  should  be 
kept  free  of  water,  that  the  air  may  "  circulate."  Roots  are 
living  structures,  and  they  need  air  just  as  the  aerial  parts  of 
the  plant  need  it.  This  is  the  reason  why  good  drainage  is 
necessary  in  a  cultivated  field,  for  drainage  carries  off  the 
free  water  which  would  drown  the  roots,  but  it  does  not 
carry  off  the  water  of  the  films.  The  ideal  arrangement  is 
for  a  well-aerated  soil  (with  no  free  water)  to  rest  upon  a  sub- 
soil that  holds  water  (like  clay),  so  that  the  rain  water  may 
''  soak  through  "  the  aerated  soil,  and  yet  be  held  near  enough 
to  it  so  that  the  films  may  be  supplied  as  they  become  thin. 
It  is  this  physical  condition  of  the  soil  that  the  farmer  must 
look  after  with  great  care. 

But  the  soil  is  not  merely  a  chemical  laboratory  supplying 
certain  substances,  and  a  physical  laboratory  making  water 
and  air  available  at  the  same  time,  but  also  an  extensive 
biological  laboratory.  In  the  chapter  dealing  with  the 
bacteria  (§  37,  p.  46),  the  extremely  important  work  of  soil 
18 


262  ELEMENTARY   STUDIES   IN   BOTANY 

bacteria  was  indicated.  Certain  very  important  substances 
needed  by  plants,  especially  substances  containing  nitrogen, 
are  put  into  usable  form  by  these  bacteria.  It  was  stated 
that  when  by  removing  crops  these  substances  become  so  di- 
minished in  amount  that  the  soil  is  said  to  become  "  poor," 
they  may  accumulate  again  by  letting  the  poor  field  "  lie 
fallow  "  until  the  bacteria  have  enriched  it,  or  by  a  "  rotation 
of  crops  "  by  means  of  which  the  same  result  is  secured 
more  rapidly.  This  shows  that  the  soil  is  the  home  of  a 
world  of  bacteria,  which  by  their  life  processes  are  putting 
materials  into  available  form  for  higher  plants. 

In  addition  to  the  soil  bacteria,  there  are  the  thready  Fungi 
called  mycorhiza  (§  40,  p.  61),  which  become  attached  to 
the  roots  of  plants  and  extend  indefinitely  through  the  soil, 
forming  a  wide  ranging  system  of  tubes  through  which  water 
may  be  brought  to  the  roots  from  regions  of  the  soil  far  be- 
yond the  reach  of  the  roots  themselves. 

The  picture  of  the  soil,  therefore,  is  that  of  a  complex 
physical,  chemical,  and  biological  laboratory,  full  of  activi- 
ties of  all  kinds.  It  is  this  delicate  and  sensitive  laboratory 
that  men  undertake  to  use  and  know  very  little  about.  They 
seek  to  "  improve  "  it  by  putting  on  all  sorts  of  "  fertilizers." 
Many  of  the  fertilizers  do  some  good ;  some  of  them  kill  the 
bacterial  life,  and  then  the  dead  soil  must  be  kept  "  fertil- 
ized " ;  none  of  them  is  used  with  sufficient  knowledge  of 
the  needs  of  the  soil.  What  any  given  soil  needs  depends 
upon  so  many  things  that  there  must  be  developed  soil 
specialists,  who  will  diagnose  soil  conditions  just  as  a  medical 
specialist  is  necessary  to  diagnose  conditions  of  the  human 
body.  Especially  is  this  true  for  soils  that  are  "  sick,"  for 
then  the  soil  is  just  as  complex  a  patient  as  is  a  sick  person. 

144.  Entrance  of  water.  —  To  obtain  water  from  the  soil, 
the  root  not  only  often  branches  profusely,  but  also  develops 
the  root-hairs  described  above  (§  140,  p.  256).  Only  in  the 
younger  portions  of  the  root,  that  is,  in  the  general  region  of 


ROOTS 


263 


the  root-hairs,  does  the  water  enter  freely.  The  root-hairs 
push  out  among  the  soil  particles  and  come  into  very  close  con- 
tact with  them,  the  particles  sometimes  being  embedded  in  the 
wall  of  the  hair  (Fig.  227).  In  this  way  the  films  of  water 
adhering  to  each  soil  particle  are  closely  applied  to  the  hair, 
and  water  passes  from  them  through  the  wall  of  the  hair  into 
its  cavity,  and  so  into  the  plant.  As 
water  enters  from  the  films  they  be- 
come thinner,  and  this  loss  is  supplied 
from  neighboring  films.  In  this  way 
a  flow  from  regions  of  the  soil  deeper 
and  more  distant  than  those  to  which 
the  root  reaches  is  set  up  toward  the 
films  losing  water.  The  water  supply 
may  not  be  able  to  make  good  such 
loss  indefinitely ;  and  if  so,  the  films 
gradually  become  thinner,  until  a 
point  is  reached  when  the  root-hair 
can  obtain  no  more  water,  the  thin 
film  holding  tenaciously  to  its  par- 
ticle of  soil.  After  the  roots  have 
obtained  all  the  water  they  can 
from  the  soil,  and  it  seems  per- 
fectly dry,  it  still  contains  two  to 
twelve  per  cent  of  water  in  the 
form  of  films. 

The  water  thus  obtained  by  the 
root-hairs  passes  inward  through 
the  cortex  ^nd  enters  the  wood  of  the  vascular  cylinder, 
and  then  is  free  to  ascend  to  the  wood  of  the  stem,  and 
so  to  the  leaves. 

145.  Entrance  of  salts.  —  In  addition  to  water,  the  soil 
supplies  chemical  substances  in  the  form  of  salts,  from  which 
the  plant  obtains  certain  elements  that  it  needs  in  the  manu- 
facture of  proteins,  as  nitrogen,  sulphur,  and  phosphorus. 


FIG.  227.  —  Root-hair  of  wheat, 
which  is  shown  to  be  an  out- 
growth of  an  epidermal  cell  in 
close  contact  with  the  soil  par- 
ticles. 


264  ELEMENTARY    STUDIES    IN   BOTANY 

The  most  important  salts  of  the  soil,  therefore,  are  nitrates, 
sulphates,  and  phosphates.  In  order  to  enter  the  root,  these 
salts  must  be  in  solution,  so  that  they  pass  in  dissolved  in 
the  water  that  enters  from  the  films  about  the  soil  particles. 
These  films,  adherent  to  the  soil  particles,  naturally  dissolve 
any  soil  material  that  is  soluble  in  water.  It  is  very  impor- 
tant to  know,  however,  that  these  dissolved  salts  are  not 
simply  swept  in  by  the  moving  water,  for  water  and  salts 
move  independently. 

The  rate  at  which  water  enters  the  plant  depends  upon 
the  rate  at  which  the  plant  is  losing  water ;  and  so  the  rate 
at  which  a  soil  salt  enters  a  plant  depends  upon  the  rate  at 
which  the  plant  is  using  it.  For  example,  if  a  soil  salt,  calico! 

A,  is  being  used  up  constantly  in  the  plant  by  being  put  into 
new  compounds,   A  will  continue  to  enter  from  the  soil. 
If,  on  the  other  hand,  a  soil-salt,  called  B,  is  not  being  used 
by  the  plant,  it  accumulates  in  the  plant  until  the  solution  of 
it  in  the  plant  is  as  concentrated  as  the  solution  of  it  in  the. 
soil  films,  and  then  no  more  of  it  can  enter,  even  if  it  does 
present  itself  to  the  root  in  solution.     This  is  what  was  once 
called  the  "  selective  power  "  of  the  root,  by  which  was  im- 
plied that  the  root  has  some  mysterious  power  of  selecting 
from  the  soil  just  what  it  needs.     In  our  illustration,  the  root 
would  seem  to  have  the  power  of  selecting  A  and  rejecting, 

B,  but  it  is  obvious  that  it  is  explained  by  a  well-known  law 
of  physics  (osmosis).1     It  follows  that  when  any  soil-salt  is 
observed  to  accumulate  in  a  plant,  it  is  an  indication  that  the 


1  Osmosis  may  be  defined  briefly  by  the  following  illustration  :  If 
a  membrane  (like  a  cell-wall)  forms  a  partition  between  two  ma*sses 
of  water,  and  sugar  is  dissolved  in  the  water  on  one  side,  it  will  pass* 
through  the  membrane  until  the  solutitJiion  both  sides'is  of  the  same 
concentration.  Therefore,  whenever  one  cell  contains  .a  s,salt  in 
greater  concentration  than  a  neighboring  cell,  there  will  be  a  move- 
ment of  the  salt  from  the  former  cell  into  the  latter ;  but  if  the  Con- 
centrations in  the  two  cells  are  the  same,  there  will  be  no  movement. 


ROOTS  265 

plant  is  not  using  it ;  and  that  the  soil-salts  the  plant  is  using 
are  not  apt  to  be  found  in  it.  This  will  explain  why  the 
chemical  analysis  of  a  plant  does  not  detect  what  it  is  using 
from  the  soil,  but  only  what  it  cannot  use. 

A  distinction  must  be  made  between  the  entrance  of  the 
salts  of  the  soil  into  the  root,  and  their  movement  through  the 
vascular  system  (xylem)  of  the  root,  stem,  and  leaves.  The 
entrance  is  through  living  cells  until  the  xylem  is  reached, 
and  then  the  movement  is  through  dead  cells.  As  has  been 
said,  a  salt  enters  a  living  cell  only  when  the  water  of  the  cell 
is  poorer  in  the  salt  tHan  the  water  outside  (osmosis) ;  but 
in  dead  tissue  (as  the  water-carrying  xylem)  osmosis  does  not 
work,  and  the  salts  dissolved  in  the  water  are  carried  along 
with  it.  When  they  reach  their  destination,  as  the  mesophyll 
cells  of  a  leaf,  they  must  pass  from  the  xylem  (of  the  veins) 
into  the  working  cells  according  to  the  law  of  osmosis.  There- 
fore, salts  enter  the  plant  by  the  selective  power  of  osmosis, 
they  are  carried  through  the  xylem  by  the  movement  of  water  f 
and  they  are  delivered  to  the  working  cells  by  the  selective 
power  of  osmosis. 

146.  Special  forms  of  roots.  —  Roots  in  soil  serve  the 
double  purpose  of  anchoring  the  plant  and  receiving  water, 
but  certain  roots  hold  other  relations  and  need  special  men- 
tion. 

(1)  Prop-roots.  —  In  certain  plants  roots  are  sent  out  from 
the  stem  or  the  branches,  and  finally  reaching  the  ground 
establish  the  usual  soil  relations.  Since  these  roots  resemble 
braces  or  props,  the  name  prop-roots  has  been  applied  to  them 
(Fig.  228).  A  very  common  illustration  is  that  of  the  corn- 
stalk, which  sends  out  such  roots  from  the  lower  nodes  of  the 
stem.  More  striking  illustrations,  however,  are  furnished 
by  the  banyan  and  the  mangrove.  The  banyan  sends  down 
from  its  wide-spreading  branches  prop-roots,  which  are 
sometimes  very  numerous.  When  they  enter  the  soil-  they 
often  grow  into  large  trunk-like  supports,  enabling  the 


266 


ELEMENTARY    STUDIES   IN   BOTANY 


branches  to  extend  over  an  extraordinary  area.  There  is 
record  of  a  banyan  cultivated  in  Ceylon  with  350  large  and 
3000  small  prop-roots,  and  able  to  cover  a  village  of  one 
hundred  huts.  The  mangrove  is  found  along  tropical  and 
subtropical  seacoasts,  and  gradually  advances  into  the  shal- 


FIG.  228.  —  A  screw-pine  with  prop-roots.  —  Photograph  by  LAND  at  Orizaba,  Mexico. 

low  water  by  dropping  prop-roots  from  its  branches  and 
entangling  the  detritus  (Fig.  229). 

(2)  Water-roots.  —  If  a  stem  is  floating,  clusters  of  whitish 
thread-like  rootlets  usually  put  out  from  it  and  dangle  in  the 
water.  Plants  which  ordinarily  develop  soil-roots,  if  brought 
into  proper  water  relations,  may  develop  water-roots.  For 


267 


268 


ELEMENTARY    STUDIES   IN   BOTANY 


instance,  willows  or  other  stream-bank  plants  may  be  so 
close  to  the  water  that  some  of  the  root  system  enters  it. 
In  such  cases  the  numerous  clustered  roots  show  their  water 
character.  Sometimes  root  systems  developing  in  the  soil 
may  enter  tile  drains,  when  water-roots  will  develop  in  such 
clusters  as  to  choke  the  drains.  The  same  bunching  of  water- 
roots  may  be  noticed 
when  a  hyacinth 
bulb  is  grown  in  a 
vessel  of  water.  It 
is  evident  that  con- 
tact with  abundant 
water  modifies  the 
formation  of  roots, 
both  as  to  number 
and  character. 

(3)  Clinging  roots. 
—  Such  roots  fasten 
the  plant  body  to 
some  support,  and 
may  be  regarded  as 
roots  serving  as  ten- 
drils. In  the  trum- 
p e t-c reeper  and 
poison-ivy  these  ten- 
dril-like roots  cling 
to  various  supports, 
such  as  stone  walls 
and  tree  trunks,  by  sending  minute  branches  into  the 
crevices.  In  such  cases,  however,  the  plant  has  also  true 
soil  roots. 

(4)  Air-roots.  —  Some  plants  have  no  soil  connection  at 
all.  In-  the  rainy  tropics,  where  it  is  possible  to  obtain 
sufficient  moisture  from  the  air,  there  are  many  such 
plants,  notable  among  which  are  the  orchids,  to  be  observed 


FIG.  230.  —  An  orchid  with  aerial  roots. 


ROOTS 


269 


in  almost  any  greenhouse.  Clinging  to  the  trunks  of  trees, 
usually  imitated  in  the  greenhouse  by  nests  of  sticks,  they 
send  out  long  roots  which  dangle  in  the  moist  air  (Fig.  230). 
Such  plants  are  called  epiphytes,  the  name  indicating  that 
they  perch  upon  other  plants  and  have  no  connection  with 
the  soil  (Fig.  231).  A  very  common  epiphyte  of  our  South- 
ern states  is  the  common  long  moss  or  black  moss  (although 


I 


FIG.  231.  —  A  group  of  epiphytes  in  a  tropical  forest.  —  After  KARSTEX  and 

SCHENCK. 


it  is  by  no  means  a  moss)  that  hangs  in  stringy  masses  from 
the  branches  of  live-oaks  and  other  trees  (Fig.  232.) 

147.  Summary.  —  The  root  receives  water  and  salts  from 
the  soil,  and  incidentally  anchors  the  plant.  The  structure 
of  its  vascular  cylinder  is  very  different  from  that  of  the  stem 
cylinder.  The  phloem  does  not  occur  between  the  xylem 


270 


ELEMENTARY    STUDIES   IN   BOTANY 


and  the  cortex,  but  phloem  strands  alternate  with  xylem 
strands  around  the  centre,  so  that  both  xylem  and  phloem 
are  in  contact  with  the  cortex.  It  is  evident  that  the  xylem 
is  to  receive  and  conduct  the  water  and  salts  from  the  soil, 
that  these  substances  must  pass  through  the  cortex  to  reach 
the  xylem,  and  that  they  must  enter  the  root  through  the 
exposed  epidermis  and  its  array  of  root-hairs. 

The  soil  is  a  complex  chemical,  physical,  and  biological 
laboratory,   where    materials   are   accumulated  and  put  in 


mm    I/-  "          '''• '  * 


FIG.  232.  —  Live-oaks  covered  with  "long  moss." 

available  form  for  plants,  and  where  hosts  of  bacteria  and 
other  fungi  are  working.  The  physical  properties  of  the  soil 
in  receiving  and  retaining  water,  the  necessity  of  drainage 
so  that  air  may  circulate  through  the  soil  freely,  the  adhe- 
sive films  of  water  about  the  soil  particles,  the  entrance  into 
the  roots  of  water  from  the  films  and  not  from  the  free  water 
of  the  soil,  are  all  physical  features  that  must  be  kept  in 
mind. 


ROOTS  271 

As  the  aerial  parts  of  the  plant  are  continually  losing  water, 
the  water  of  the  soil  can  always  enter  the  root  freely.  The 
salts  of  the  soil  must  be  dissolved  in  the  water  before  entering, 
and  even  when  dissolved  they  can  enter  only  in  case  they  are 
being  used  by  the  plant  and  therefore  changed. 


CHAPTER  XIV 
PLANT  ASSOCIATIONS 

148.  General    statement.  —  In    the    preceding    chapters 
plants  have  been  studied  as  individuals  that  have  certain 
structures  and  that  live  and  work  in  certain  conditions. 
There  is  another  aspect  of  plants  that  must  be  considered, 
when  one  regards  them  as  "  clothing  "  the  earth.     This  is 
the  broadest  view  of  plants,  and  it  requires  a  great  deal  of 
training  to  appreciate  it  fully.     The  purpose  of  the  present 
chapter,  therefore,  is  not  to  discuss  this  subject,  but  to  give 
the  elementary  student,  with  some  knowledge  of  plants  as 
individuals,  a  glimpse  of  it.     The  two  aspects  of  plants  re- 
ferred to  may  be  illustrated  by  the  two  methods  of  studying 
people  :  they  may  be  studied  as  individuals  engaged  in  various 
kinds  of  work,  or  they  may  be  studied  as  groups  associated 
in  villages  and  cities.     It  is  true  that  the  earth  is  covered 
by  individual  plants,  but  it  is  also  true  that  these  plants  are 
associated  together  in  various  ways,  forming  what  may  be 
called  plant  communities.     It  is  this  community  life  of  plants 
that  is  to  be  considered  in  the  present  chapter. 

149.  Plant  associations.  —  It  is  a  fact  of  common  obser- 
vation that  plants  are  not  scattered  indiscriminately  over  the 
surface  of  the  earth,  regardless  of  one  another  and  of  the 
conditions  for  growth.     It  is  recognized,  for  example,  that 
there  are  forests,  prairies,  plains,  and  swamps,  each  one  of 
which  represents  an  association  of  plants  that  characterizes 
it.     Into  each  association  certain  plants  are  admitted,  and 
from  each  association  many  plants  are  excluded.     That  is, 

272 


PLANT    ASSOCIATIONS  273 

we  have  come  to  recognize  that  certain  plants  are  naturally 
associated,  because  they  grow  in  the  same  conditions.  Any 
set  of  conditions  for  plants  is  said  to  be  a  habitat,  that  is,  a 
place  that  certain  plants  inhabit.  Therefore,  each  kind  of 
habitat  has  its  own  association  of  plants,  and  a  plant  associa- 
tion may  be  denned  as  an  association  of  plants  growing  to- 
gether in  the  same  habitat. 

150.  Determining  factors.  —  Since  different  kinds  of 
habitats  are  characterized  by  different  kinds  of  plant  associa- 
tions, it  is  important  to  discover  the  things  that  make  habi- 
tats different,  that  is,  the  factors  that  determine  the  char- 
acter of  a  habitat  in  reference  to -plants.  It  must  not  be 
supposed  that  all  the  determining  factors  have  been  dis- 
covered or  that  the  relative  importance  of  those  that  are 
known  is  appreciated  fully. 

The  most  conspicuous  determining  factor,  and  perhaps  the 
most  important  one,  is  available  water,  that  is,  water  in  a 
condition  to  be  used  by  plants.  The  range  of  water-supply 
may  be  said  to  extend  from  100  per  cent,  in  which  case  the 
plants  would  be  submerged,  to  5  or  even  2  per  cent,  in  which 
case  the  habitat  would  be  called  a  "  desert."  Plants  differ 
as  to  the  amount  of  water  they  must  have,  and  therefore  a 
plant  that  needs  a  habitat  with  at  least  a  50  per  cent  water- 
supply  could  not  live  in  the  habitats  with  a  less  supply,  and 
might  not  be  able  to  endure  a  much  greater  supply.  In  this 
way,  the  possible  range  of  water-supply  may  be  thought  of  as 
a  violin  string,  which  can  be  made  to  produce  many  different 
tones,  and  each  "  tone  "  in  our  range  of  water-supply  stands 
for  a  different  habitat  and  a  different  plant  association. 

.  Another  determining  factor  is  the  temperature,  and  every 
one  knows  that  some  plants  need  more  heat  than  others.  The 
range  of  temperature  in  which  plants  can  work  may  be  stated 
roughly  as  extending  from  120°  F.  to  32°  F.  (freezing  point). 
Of  course  many  plants  can  endure  lower  temperatures,  for 
they  survive  the  winters,  but  the  temperature  that  deter- 


274  ELEMENTARY   STUDIES   IN   BOTANY 

mines  a  plant  association  is  the  working  temperature.  The 
range  of  temperature  may  be  likened  to  a  second  violin 
string  that  can  produce  different  tones,  each  temperature 
"  tone  "  standing  for  a  different  plant  association. 

These  two  determining  factors  (water  and  temperature) 
introduce  the  idea  of  combinations  of  factors.  For  example, 
two  violin  strings  make  possible  a  far  greater  variety  of  tones 
when  used  in  combination  than  when  used  singly.  In  the 
same  way  the  combination  of  two  determining  factors  mul- 
tiplies plant  habitats  and  associations.  If  there  is  a  com- 
bination of  maximum  water-supply  and  maximum  tempera- 
ture, the  plant  association  will  be  a  tropical  jungle ;  but 
if  there  is  a  combination  of  minimum  water  supply  and 
maximum  temperature,  the  habitat  will  be  a  desert.  This 
indicates  the  numbers  of  different  plant  associations  that  vari- 
ous combinations  of  factors  make  possible. 

Other  determining  factors,  such  as  soil,  light,  wind,  etc., 
have  been  studied,  but  they  do  not  need  to  be  discussed  here. 
They  suggest,  however,  that  the  different  kinds  of  plant  as- 
sociations may  be  very  numerous,  for  if  a  violin  with  two 
strings  can  make  possible  a  large  number  of  combinations, 
what  must  be  the  possible  number  of  combinations  when  the 
violin  has  six  or  more  (probably  many  more)  strings?  This 
simply  means  that  each  plant  association  has  an  individuality 
of  its  own,  just  as  each  town  or  city  has  its  own  individuality. 
Therefore,  wherever  one  goes,  he  meets  with  new  kinds  of 
plant  associations,  just  as  he  meets  with  new  kinds  of  cities 
wherever  he  travels. 

151.  Some  features  of  a  plant  association.  —  When  a  plant 
association  is  visited,  it  may  be  looked  upon  as  a  community 
whose  population  consists  of  plants.  There  are  certain 
general  features  in  the  community  life  of  such  a  population 
that  become  evident  at  once. 

One  of  the  most  obvious  facts  is  that  certain  individuals 
dominate  and  give  tone  to  the  community.  For  example, 


PLANT    ASSOCIATIONS  275 

a  forest  association  is  dominated  by  the  trees,  and  often  by 
one  or  two  kinds  of  trees.  This  is  so  evident  that  most 
people  think  of  a  forest  as  consisting  of  trees  alone,  when  in 
fact  they  are  only  part  of  a  large  population.  In  the  same 
way,  a  meadow  is  dominated  by  grasses,  so  that  to  many  it 
seems  to  be  almost  exclusively  a  grass  population.  Thus 
each  association  is  apt  to  have  its  dominating  individuals 
that  characterize  it.  This  fact  has  a  very  interesting  cor- 
ollary. The  rest  of  the  plant  population  must  adjust  itself 
to  the  dominant  individuals.  .For  example,  in  the  forest 
population,  the  other  plants  must  adjust  themselves  to  the 
dominating  trees.  Very  many  of  them  are  so  constituted 
that  they  can  live  in  the  shade  of  trees ;  while  others,  like  the 
"  spring  flowers,"  by  means  of  underground  storage  of  food 
in  roots  or  stems,  can  spring  up  rapidly  and  come  into  flower 
in  the  short  period  between  the  first  warm  days  of  spring  and 
the  full  foliage  of  the  trees,  thus  finishing  their  work  before 
the  shade  becomes  dense. 

Another  notable  feature  of  a  plant  community  is  that  the 
nearest  relatives  are  the  keenest  competitors.  If  a  certain 
kind  of  plant  has  established  itself  in  a  community,  it  is 
very  difficult  for  a  nearly  related  plant  to  obtain  a  foothold. 
It  must  not  be  thought  that  the  "  competition  "  referred 
to,  whatever  it  may  be,  is  of  the  active  sort,  but  the  word 
at  least  figuratively  describes  a  situation.  This  fact  con- 
tains some  very  practical  suggestions.  Our  worst  "  weeds  " 
are  not  members  of  our  native  population,  but  immigrants. 
In  various  ways,  the  native  plants  of  foreign  countries  be- 
come introduced  into  America.  If  they  find  near  relatives 
in  our  native  population,  they  are  not  heard  of  as  weeds ; 
but  if  they  find  no  near  relatives,  they  are  probably  freer 
from  competition  than  they  were  in  their  native  country, 
and  may  become  a  pest.  The  important  suggestion,  how- 
ever, is  that  the  more  kinds  of  plants  there  are  on  a  given 
area,  the  larger  will  be  the  total  plant  population.  For 


276  ELEMENTARY    STUDIES   IN   BOTANY 

example,  compare  the  number  of  individual  plants  in  a  well- 
kept  corn-field,  in  which  we  are  trying  to  cultivate  as  many 
individuals  of  one  kind  as  possible,  with  the  number  of  in- 
dividuals (population)  on  an  equal  area  in  nature.  In  the 
former  case,  the  individuals  stand  well  apart  and  are  com- 
paratively few ;  while  in  the  latter  case  they  stand  thickly 
together  and  are  many  times  more  numerous.  In  both 
cases,  the  plants  are  "  doing  well."  The  Chinese  have  taken 
advantage  of  this  fact  in  their  cultivation  of  plants,  raising 
two  or  three  different  crops  simultaneously  on  the  same  area, 
and  thus  increasing  the  total  population  and  of  course 
the  total  yield.  In  cultivating  only  one  kind  of  plant  at 
a  time  on  an  area,  therefore,  we  are  reducing  the  possible 
plant  population  to  its  minimum. 

152.  Succession  of  plant  associations.  —  The  most  im- 
portant fact  in  reference  to  a  plant  association  is  that  it  is 
not  permanent  on  a  given  area.  In  general,  when  a  plant 
association  lives  for  a  time  upon  an  area,  that  area  becomes 
increasingly  unfavorable  to  it,  until  gradually  it  is  succeeded 
by  another  plant  association.  Almost  any  plant  associa- 
tion finally  makes  conditions  unfit  for  itself,  and  at  the  same 
time  more  fit  for  some  other  association.  This  succession 
of  plant  associations  may  be  illustrated  by  the  succession 
of  human  communities.  Pioneer  conditions  bring  together 
a  characteristic  association  of  individuals,  but  the  conditions 
do  not  remain  pioneer,  and  become  favorable  for  another 
association  of  individuals,  and  this  kind  of  succession  may 
go  on,  until  the  series  of  associations  can  be  traced  from  the 
pioneer  association  to  the  metropolitan  association.  This 
means  that  each  plant  association  can  reveal  the  succession 
of  associations  that  preceded  it  and  also  the  succession  of 
associations  that  will  succeed  it.  In  other  words,  the  most 
important  thing  about  a  plant  association  is  the  history  and 
prophecy  it  contains. 

It  is  evident  that  there  may  be  many  kinds  of  succession, 


PLANT   ASSOCIATIONS  277 

dependent  upon  the  habitat.  The  start  may  be  on  bare 
rock,  on  sand,  on  clay,  in  a  drained  swamp,  or  in  an  un- 
drained  swamp,  and  then  each  kind  of  succession  will  follow. 
It  is  also  evident  that  the  succession  cannot  go  on  indefinitely, 
but  that  some  final  association  will  be  reached  which  is  called 
the  climax  association,  for  that  region.  In  general,  some 
type  of  forest  is  the  climax  association,  but  there  are 
obvious  reasons  why  that  type  cannot  be  reached  in  certain 
regions. 

153.  Forest  succession.  —  Since  forests  represent  the 
most  important  natural  vegetation,  an  illustration  of  forest 
succession  will  be  given.  It  will  serve  to  illustrate  not  only 
an  important  succession,  but  also  the  facts  that  must  be  con- 
sidered in  any  effective  study  of  forestry.  One  of  the  best 
known  forest  regions  is  the  white  pine  region  of  Northern 
Michigan,  from  which  the  trees  have  been  swept,  with  no 
thought  of  their  continuance,  and  the  evolution  of  this  forest 
will  indicate  the  forest  problems  in  general. 

The  succession  of  plant  associations  which  led  up  to  the 
white  pine  forests  started  on  sand,  rock,  clay,  or  in  swamps, 
but  the  series  beginning  on  a  sandy  beach  will  be  used  in 
the  illustration.  The  first  stage  was  the  lower  beach, 
washed  by  the  summer  waves,  and  therefore  with  no  vegeta- 
tion, but  with  an  accumulation  of  sandy  soil.  The  second 
stage  was  the  middle  beach,  rising  higher  above  the  water, 
and  therefore  washed  only  by  the  larger  winter  waves.  This 
freedom  from  waves  during  the  summer  permitted  the  growth 
of  certain  annual  plants,  whose  bodies  added  some  humus 
to  the  sand.  The  third  stage  was  the  fossil  beach,  that  is, 
a  beach  that  was  once  washed  by  the  waves,  but  is  now  beyond 
their  reach.  This  ^continual  freedom  from  wave  action  per- 
mitted the  growth  of  more  plants,  and  therefore  resulted  in 
the  accumulation  of  more  humus,  but  the  soil  would  still 
have  looked  rather  bare,  as  the  plants  would  not  cover  the 
surface.  The  fourth  stage  was  made  possible  by  the  accu- 
19 


278  ELEMENTARY   STUDIES   IN   BOTANY 

mulation  of  humus,  and  it  is  called  the  heath  stage,  for  plants 
of  the  heath  family  and  their  associates  occupied  the  ground. 
At  this  stage,  for  the  first  time,  the  plants  covered  the  ground 
so  thickly  that  competition  among  individuals  began. 

With  the  further  accumulation  of  humus,  the  fifth  stage 
became  possible,  that  is,  the  pine  forest  stage.  Gradually 
the  pines  invaded  the  heath,  first  the  jack  pine,  then  the  red 
pine,  and  finally  the  white  pine.  It  was  at  this  stage  that 
men  caught  the  succession  and  destroyed  the  pines.  When 
a  forest  fire  swept  through  the  pine  forest,  it  not  only  checked 
the  succession,  but  often  set  it  back.  If  the  fire  was  pro- 
longed and  intense,  it  not  only  destroyed  trees,  but  also 
much  of  the  humus,  and  in  such  a  case  the  succession  might 
be  set  back  to  the  heath  stage.  This  would  mean  a  long 
accumulation  of  humus  before  the  pine  forest  could  come  in 
again. 

But  the  important  fact  is  that  the  white  pine  forest  is 
not  the  climax  forest  for  that  region,  for  it  has  the  curious 
habit  of  what  may  be  called  race  suicide.  Its  seeds  do  not 
germinate  well  and  its  seedlings  do  not  thrive  in  the  shade, 
so  that  when  a  deeply  shaded  white  pine  forest  is  established, 
it  cannot  perpetuate  itself.  But  this  shade  is  favorable  to 
the  seeds  and  seedlings  of  the  maple  and  beech,  and  therefore 
these  trees  gradually  supplant  the  white  pine,  and  the  maple- 
beech  forest  (a  hard-wood  forest)  is  the  climax  association 
for  that  region.  It  follows  that  the  problem  of  forestry  in 
the  white  pine  region  is  not  merely  a  fight  against  the  dev- 
astation of  men,  but  more  fundamentally  a  fight  against 
the  race  suicide  of  the  white  pines  and  against  the  encroach- 
ment of  the  hard- wood  trees. 

This  is  an  illustration  of  but  a  single  forest  succession  out 
of  a  great  many  that  forestry  must  recognize.  For  example, 
in  Oregon  and  Washington,  where  the  conifer  forests  are  so 
conspicuous,  they  are  the  climax  type,  and  there  is  no  danger 
of  an  invasion  by  hardwood  trees.  The  conifers  of  that  region 


PLANT   ASSOCIATIONS  279 

do  not  commit  race  suicide,  and  the  deciduous  (hard-wood) 
trees  are  not  favored  by  the  winter  rains  and  dry  summers. 

154.  Some  conspicuous  plant  associations.  —  It  has  be- 
come customary  to  group  all  plant  associations  under  three 
heads,  based  on  the  water-supply  of  the  habitat.  Hydro- 
phytes ("  water  plants  ")  are  plants  that  grow  in  water  or 
in  very  wet  soil,  and  their  associations  are  "  hydrophytic 
associations."  Xerophytes  ("  dry  plants  ")  are  plants  that 
grow  in  conditions  of  scanty  water-supply,  and  their  associa- 
tions are  "  xerophytic  associations."  Mesophytes  ("  medium 
plants  ")  are  plants  that  grow  in  conditions  of  medium 
water-supply,  and  their  associations  are  "  mesophytic  asso- 
ciations." 

It  should  be  noted  that  the  mesophytic  conditions  are 
those  used  for  cultivating  plants,  such  land  being  said  to  be 
"  arable."  If  the  conditions  are  hydrophytic,  the  land  is 
drained  before  cultivation ;  if  the  conditions  are  xerophytic 
and  there  is  sufficient  soil  accumulation,  the  land  is  irrigated. 
The  same  processes  are  going  on  in  nature.  If  a  succession 
of  societies  starts  in  a  pond  or  swamp  (hydrophytic),  the 
conditions  gradually  become  more  and  more  mesophytic, 
until  finally  mesophytic  associations  appear.  If  a  succes- 
sion starts  on  a  bare  rock  or  sand  (xerophytic) ,  through  the 
accumulation  of  humus  and  the  increase  of  shading,  the  con- 
ditions gradually  become  more  and  more  mesophytic,  until 
finally  mesophytic  associations  appear.  This  means  that 
where  conditions  are  not  mesophytic  already,  the  natural 
succession  of  societies  tends  to  make  them  so. 

From  what  has  been  said  of  plant  associations,  it  is  evident 
that  they  are  far  too  numerous  to  permit  in  this  connection 
a  description  of  even  the  most  conspicuous  ones.  The  best 
that  can  be  done  is  to  select  from  among  the  most  con- 
spicuous associations  a  few  types  that  will  emphasize  what 
is  meant  by  plant  associations.  It  must  be  understood  that 
this  is  not  to  be  a  study  of  these  associations,  for  such  study 


280 


ELEMENTARY    STUDIES   IN   BOTANY 


requires  a  great  deal  of  training,  but  it  is  to  be  merely  an 
introduction  to  certain  associations. 

Along  the  low  shores  of  small  lakes,  it  is  very  common  to 


FIG.  233.  —  A  reed  swamp  near  Chicago. 


see  in  the  shallow  margin  a  high  fringe  of  reed-like  plants, 
among  which  wild  rice,  bulrushes,  and  cat-tails  dominate 
(Fig.  233) .  This  kind  of  association  is  known  as  a  reed  swamp, 


281 


282  ELEMENTARY   STUDIES   IN   BOTANY 

and  its  plants  have  been  called  the  pioneers  of  land  vegeta- 
tion ;  for  their  growth  and  the  entangled  detritus  make  the 
water  more  and  more  shallow,  until  finally  the  reed  plants 
are  compelled  to  migrate  into  deeper  water.  In  this  way 
small  lakes  and  ponds  may  become  converted  first  into 
ordinary  swamps,  and  finally  into  wet  meadows.  Instances 
of  nearly  reclaimed  ponds  may  be  found,  where  bulrushes, 
cat-tails,  and  reed  grasses  still  occupy  certain  wet  spots, 
but  are  shut  off  from  further  migration. 

In  many  regions,  especially  in  our  northern  states,  there 
is  a  peculiar  kind  of  swamp  association,  characterized  by  the 
abundant  growth  of  the  bog  moss  or  peat  moss,  and  de- 
veloped in  undrained  swamps.  Growing  out  of  the  springy 
moss  turf  there  are  numerous  peculiar  plants,  such  as  heaths 
and  orchids,  and  the  curious  carnivorous  plants  (§  127, 
p.  218).  Often  trees  encroach  upon  peat  bogs  and  a  swamp 
forest  is  the  result.  The  chief  types  in  this  case  are  the  coni- 
fers, and  on  this  bog-moss  foundation  there  occur  larches, 
certain  hemlocks  and  pines,  junipers,  etc.  The  larch  or 
tamarack  is  a  very  common  swamp  tree  of  the  northern 
regions,  usually  occurring  in  small  patches ;  while  the  larger 
swamp  forests  are  composed  of  dense  growths  of  hemlocks, 
pines,  etc.  (Fig.  234). 

The  two  illustrations  just  given  are  from  hydrophytic  asso- 
ciations, but  the  swamp  forest  is  approaching  the  mesophytic 
conditions. 

Plant  associations  inhabiting  dry,  sandy  ground  are  very 
common,  but  perhaps  the  most  extreme  type  of  sand  as- 
sociations is  that  which  inhabits  dunes,  and  may  be  called 
dune  associations.  On  certain  borders  of  the  Great  Lakes 
and  of  sea  coasts,  beyond  the  beach,  the  dunes  occur.  They 
are  billows  of  sand  formed  by  the  prevailing  winds,  and  in 
many  cases  they  are  continually  changing  their  form  and  are 
frequently  moving  landward  (Fig.  235) .  In  the  case  of  these 
moving  dunes  a  peculiar  type  of  vegetation  is  demanded, 


PLANT   ASSOCIATIONS 


283 


and  very  few  plants  are  able  to  live  in  such  severe  con- 
ditions. 

One  of  the  greatest  of  plant  associations  is  that  which 
occupies  the  plains  in  the  interior  of  continents,  where  dry 
air  and  wind  prevail.  The  plains  of  the  United  States 
extend  from  about  the  one-hundredth  meridian  westward  to 
the  foothills  of  the  Rocky  Mountains.  Similar  great  areas 


FIG.  235.  —  Dunes  of  Lake  Michigan  encroaching  upon  the  land,  in  this  case  diverting 

Calumet  River. 

are  represented  by  the  steppes  of  Siberia,  and  in  the  interior 
of  all  continents.  On  the  plains  of  the  United  States  the 
characteristic  plant  forms  are  bunch-grasses  (grasses  that 
grow  in  tufts  and  do  not  form  turf)  and  the  low  grayish 
shrubs  called  sagebrush. 

In  passing  southward  on  the  plains  of  the  United  States, 
the  conditions  are  observed  to  become  drier,  until  the  cactus 
deserts  are  reached.  This  region  begins  in  western  Texas, 
New  Mexico,  Arizona,  and  southern  California,  and  stretches 
far  southward  into  Mexico.  This  vast  arid  region  has  de- 


284  ELEMENTARY   STUDIES   IN   BOTANY 

veloped  a  peculiar  flora,  which  contains  our  most  highly 
specialized  drought  plants.  The  numerous  forms  of  cactus 
are  the  most  characteristic,  and  associated  with  them  are 
the  yuccas  and  agaves.  Not  only  is  the  equipment  for  check- 
ing transpiration  and  for  retaining  water  of  the  most  ex- 
treme kind,  but  also  there  is  developed  a  remarkable  armature 
of  spines. 

The  dune  associations,  plains,  and  cactus  deserts  are  illus- 
trations of  xerophytic  associations,  but  even  more  extreme 
xerophytic  conditions  occur  in  connection  with  bare,  exposed 
rocks,  and  in  the  subtropical  desert  regions  (as  the  desert  of 
Sahara) . 

Three  conspicuous  kinds  of  mesophytic  associations  may 
be  selected  as  illustrations,  associations  that  require  a  medium 
amount  of  moisture,  a  more  or  less  evenly  distributed  pre- 
cipitation, and  a  soil  rich  in  humus. 

A  very  characteristic  mesophytic  association  is  the  meadow, 
by  which  is  meant  areas  of  natural  meadow,  not  to  be  con- 
fused with  artificial  areas  of  the  same  name  under  the  con- 
trol of  man.  The  appearance  of  such  an  area  hardly  needs 
description,  as  the  vegetation  is  a  well-known  mixture  of 
grasses  and  flowering  herbs,  the  former  usually  predominat- 
ing. Such  meadows,  of  large  or  small  extent,  are  very 
common  in  connection  with  forest  areas  and  on  the  flood-plains 
of  streams  (Fig.  236). 

The  greatest  meadows  of  the  United  States  are  the  prairies, 
which  extend  in  general  from  the  Missouri  eastward  to  the 
forest  region  of  Illinois  and  Indiana.  The  vegetation  of  the 
prairies  is  usually  composed  of  tufted  grasses  and  peren- 
nial flowering  herbs.  Unfortunately,  most  of  the  natural 
prairie  has  been  replaced  by  farms,  and  the  characteristic 
prairie  plants  are  not  easily  seen.  The  flowering  herbs  are 
often  very  tall  and  coarse,  but  have  brilliant  flowers,  as 
asters,  goldenrods,  rosinweeds,  lupines,  etc.  The  origin  of 
the  prairie  has  long  been  a  vexed  question,  which  has  usually 


285 


286  ELEMENTARY   STUDIES   IN   BOTANY 

taken  the  form  of  an  inquiry  into  the  conditions  which  for- 
bid the  growth  of  a  natural  forest.  Prairies  are  of  two  kinds 
at  least;  those  due  to  soil  conditions  and  those  due  to  cli- 
matic conditions.  The  former  are  characteristic  of  the  eastern 
prairie  region,  and  appear  in  scattered  patches  through  the 
forest  region  as  far  east  as  Ohio  and  Kentucky.  They  are 
probably  best  explained  as  representing  old  swamp  areas, 
which  in  a  still  more  ancient  time  were  ponds  or  lakes.  All 
the  prairies  of  the  Chicago  area  are  evidently  of  this  type, 
being  associated  with  former  extensions  of  Lake  Michigan. 
The  climatic  prairies  are  characteristic  of  the  western  prairie 
region,  and  are  more  puzzling  than  the  others.  Among  the 
several  explanations  suggested,  perhaps  the  most  prominent 
is  that  which  regards  the  absence  of  a  natural  forest  on  the 
western  prairies  as  due  to  the  prevailing  dry  winds.  The 
extensive  plains  farther  west  develop  the  strong  and  dry 
winds  that  sweep  over  the  prairies,  and  this  brings  extremes 
of  heat  and  drought,  in  spite  of  the  character  of  the  soil. 
In  such  conditions  a  seedling  tree  could  not  establish  itself. 
If  it  is  protected  through  this  tender  period,  it  can  maintain 
itself  afterward.  These  prairies,  therefore,  represent  a  sort 
of  broad  beach  between  the  western  plains  and  the  eastern 
prairies  and  forests. 

The  climax  type  of  plant  association  in  temperate  regions 
is  the  deciduous  forest.  Such  forests  may  be  pure  or  mixed. 
A  common  type  of  pure  forest  is  the  beech  forest,  which  is 
a  dark  forest,  the  wide-spreading  branches  of  neighboring 
trees  overlapping  so  as  to  form  a  dense  shade  (Fig.  237). 
In  such  a  forest,  therefore,  there  is  little  or  no  undergrowth. 
Another  pure  forest,  which  belongs  to  drier  areas,  is  the  oak 
forest,  which  is  a  light  forest,  permitting  access  of  light  for 
lower  plants.  In  such  a  forest,  therefore,  there  is  usually 
more  or  less  undergrowth.  The  typical  American  deciduous 
forest,  however,  is  the  mixed  forest,  made  up  of  many  vari- 
eties of  trees,  such  as  beech,  oak,  elm,  walnut,  hickory, 


287 


288 


ELEMENTARY    STUDIES   IN   BOTANY 


maple,  gum,  etc.  Deciduous  forests  may  be  roughly  grouped 
also  as  upland  and  flood-plain  (river  bottom)  forests,  the  for- 
mer being  less  luxuriant  and  containing  fewer  types,  the  lat- 
ter being  the  highest  type  of  forest  growth  in  its  region. 

The  forests  of  the  rainy  tropics,  called  rainy  tropical 
forests,  may  be  regarded  as  the  climax  of  the  world's  vegeta- 
tion (Fig.  238),  for  the  conditions  favor  constant  plant 


FIG.  238.  —  A  tropical  forest.  —  Photograph  by  LAND  near  Xalapa,  Mexico. 

activity  a  the  highest  possible  pressure.  Such  great  forest 
growths  are  found  within  the  region  of  the  trade-winds, 
where  there  is  heavy  rainfall,  great  heat,  and  very  rich  soil, 
as  in  the  East  Indies,  and  along  the  Amazon  and  its  tributaries. 
So  abundant  is  the  precipitation  that  the  air  is  often  saturated 
and  the  plants  drip  with  the  moisture.  In  a  great  mixed 
tropical  forest  there  is  no  regular  period  for  the  development 
or  fall  of  leaves,  and  hence  there  is  no  time  of  bare  forests 
or  of  forests  just  putting  out  leaves.  Leaves  are  continually 
being  shed  and  formed,  but  the  trees  always  appear  in  full 


PLANT   ASSOCIATIONS  289 

foliage.  The  density  of  growth  is  always  remarkable,  re- 
sulting in  a  gigantic  jungle,  with  plants  at  every  level,  inter- 
laced by  great  vines  and  covered  by  perching  plants ;  in 
fact,  all  the  space  between  the  ground  and  the  tree-tops  seems 
to  be  packed  with  plants. 

155.  Summary.  —  Different  areas  support  different  kinds 
of  plants,  and  plants  naturally  assembled  on  any  area  form 
a  natural  association.  Each  association  of  plants  has  its 
own  habitat.  The  chief  features  of  a  habitat  that  determine 
what  plants  shall  occupy  it  are  available  water,  temperature, 
soil,  exposure  to  light,  prevailing  winds,  etc. 

Certain  kinds  of  plants  dominate  and  give  character  to 
the  association  established  upon  a  habitat.  The  other  mem- 
bers of  the  association  must  adjust  themselves  to  the  domi- 
nant plants,  and  learn  to  live  under  whatever  conditions 
the  dominant  plants  permit.  In  any  association  of  plants 
the  plant  population  is  in  proportion  to  the  number  of 
kinds  of  plants  included  in  the  association.  A  single  kind 
of  plant  cannot  produce  as  many  individuals  on  a  given 
area  as  can  several  kinds  of  plants. 

The  most  important  fact  about  plant  associations  is  their 
succession,  which  means  that  an  association  makes  a  habitat 
unfit  for  itself  and  more  fit  for  some  other  association.  The 
succession  on  any  area  ends  in  a  climax  association  for  that 
region,  and  in  general  the  climax  is  some  kind  of  forest 
association. 


PART  II 
PLANTS  IN   CULTIVATION 


NOTE   TO   TEACHERS 

IN  addition  to  what  has  been  said  in  the  general  preface 
concerning  the  purpose  of  Part  II,  the  attention  of  the 
teacher  should  be  called  to  a  few  practical  suggestions. 

Such  a  subject  as  plants  in  cultivation  must  include  a 
much  wider  range  of  plants  than  those  commonly  recognized 
as  producing  "  crops."  It  must  include  not  only  the  products 
of  agriculture,  but  also  the  plants  that  enter  conspicuously 
into  our  experience,  either  as  plants  (cultivated  flowers)  or 
as  plant  products  (lumber  and  fibers).  This  more  extensive 
contact  with  the  commercially  important  plants  not  only 
gives  a  more  adequate  conception  of  the  uses  of  plants,  but 
also  makes  it  possible  to  supplement  the  relatively  poor 
facilities  for  agricultural  operations  in  connection  with  city 
schools,  by  the  exceptional  facilities  of  city  schools  to  observe 
a  wide  range  of  plant  products  in  the  city  markets. 

It  will  be  of  very  great  service  for  the  teacher  to  apply 
to  the  Agricultural  Experiment  Station  of  the  state  for  ma- 
terial and  for  information.  A  great  number  of  bulletins  are 
published  by  the  stations,  dealing  with  the  conspicuous 
crops  of  the  state,  and  giving  suggestions  as  to  their  cultiva- 
tion. By  means  of  these  bulletins,  a  more  intensive  study 
of  the  state  crops  can  be  made  than  is  suggested  by  the  book, 
which  cannot  emphasize  all  the  crops  of  all  the  states,  but 
which  suggests  how  to  begin  their  study. 

In  addition  to  state  bulletins  and  local  information,  some 
standard  works  of  reference  should  be  available,  which  can 
be  consulted  for  fuller  details  than  any  text-book  can  give. 
A  very  useful  work  of  this  kind  is  BAILEY'S  Cyclopedia  of 
American  Horticulture  (4  vols.),  which  contains  all  the  infor- 
20  293 


294  NOTE   TO  TEACHERS 

mation  that  could  be  needed  in  reference  to  the  cultivation  of 
plants,  except  in  reference  to  the  cereals.  The  cereals  are 
likely  to  be  well  cared  for  by  the  station  bulletins. 

The  teacher  must  remember  that  while  much  that  this  part 
contains  and  suggests  will  have  to  be  given  as  information, 
there  is  a  large  opportunity  to  do  practical  work.  This  work 
may  be  of  the  most  varied  kinds,  as  growing  plants  in  the 
schoolroom  or  school  garden,  assigning  work  in  home  gardens, 
inspecting  crops  in  fields  and  market  gardens,  examining  and 
learning  to  recognize  the  trees  in  common  cultivation, 
especially  those  used  for  street-planting,  visiting  markets  and 
inquiring  as  to  the  sources  and  seasons  of  the  various  fruits 
and  vegetables,  visiting  florists  and  learning  to  recognize 
the  common  ornamental  plants,  looking  over  cultivated 
plants  for  indications  of  disease,  etc.  In  short,  the  oppor- 
tunity is  ample  for  developing  an  experience  of  great  practical 
value,  which  will  extend  further  than  merely  the  cultivation 
of  plants,  and  will  include  the  personal  interests  of  every 
pupil. 


CHAPTER   I 
INTRODUCTION 

1.  The  use  of  plants.  —  In  Part  I  a  brief  account  of  the 
structure  of  plants  and  of  their  principal  activities  is  given. 
This  forms  the  basis  of  the  science  of  Botany  and  develops 
some  knowledge  of  a  very  conspicuous  part  of  nature.  But 
there  is  another  aspect  of  plants,  which  does  not  deal  with 
them  as  a  source  of  knowledge,  but  as  things  of  great  use. 
Comparatively  few  people  are  interested  in  knowing  about 
plants,  but  every  one  is  interested  in  using  plants. 

When  one  recalls  the  uses  made  of  plants,  he  realizes  that 
the  human  race  is  very  dependent  upon  them.  Of  all  the 
uses  to  which  plants  are  put,  however,  the  most  conspicuous 
is  their  use  as  a  source  of  food.  In  fact,  even  the  meat  we 
use  is  obtained  from  animals  that  feed  upon  plants ;  so  that, 
directly  or  indirectly,  all  food  is  derived  from  plants.  It  is 
evident  that  this  must  be  true,  because,  as  was  stated  in 
Part  I,  green  plants  are  the  only  living  things  that  can  manu- 
facture food  out  of  raw  materials ;  that  is,  materials  that  are 
not  food.  It  is  upon  this  food  manufacture  that  all  plants 
and  animals  depend;  the  green  plants  use  the  food  they 
manufacture  for  themselves,  while  plants  that  are  not  green 
(as  mushrooms)  and  all  animals  depend  upon  the  food  that 
green  plants  manufacture  in  excess  of  their  own  need. 

The  most  primitive  men,  of  course,  as  they  roamed  about, 
obtained  their  plant  food  from  wild  plants.  Even  yet  there 
is  much  "  wild  food  "  used,  notably  such  berries  as  black- 
berries, raspberries,  huckleberries,  etc.  An  important  stage 
in  the  progress  of  the  human  race  was  when  men  began  to 
select  certain  of  the  wild  plants  for  cultivation.  The  rais- 

295 


296  ELEMENTARY  STUDIES  IN  BOTANY 

ing  of  crops  checked  the  roaming  of  men,  and  they  began 
to  "  settle  down  "  and  cultivate  definite  areas  of  land.  In 
this  way,  tribes  of  wandering  hunters  became  transformed 
gradually  into  groups  of  farmers.  One  of  the  most  ancient 
occupations  of  men,  therefore,  was  the  cultivation  of  plants. 
When  one  considers  the  many  thousands  of  kinds  of  plants, 
it  is  a  surprise  that  only  a  few  hundred  have  been  selected  for 
cultivation  in  the  whole  history  of  the  human  race.  The 
reason  is  that  the  few  selected  have  supplied  the  needs  of  the 
human  race,  but  there  is  a  rich,  unworked  mine  in  the  thou- 
sands of  plants  that  have  not  yet  been  brought  into 
cultivation. 

2.  Cultivated  plants.  —  The  first  plants  cultivated  seem 
to  have  been  the  cereals.     The  grains  of  certain  wild  grasses 
attracted  attention  as  suitable  for  food  and  easy  of  cultiva- 
tion, and  thus  the  cultivation  of  wheat,  oats,  barley,  and  rye 
began.     These  grasses,  apparently  the  first  selected,  have 
continued  to  be  cultivated  as  exceedingly  important  food 
plants.     Later,  other  grasses  came  into  cultivation  as  food 
plants,  notably  rice  and  corn,  and  thus  our  most  important 
cereals  were  assembled.     A  further  addition  to  the  list  of 
cultivated  grasses  was  made  when  the  need  for  crops  of  hay 
as  food  for  domesticated  animals  was  developed.     For  this 
purpose,  suitable  meadow  grasses  were  selected,  but  they  have 
not  been  cultivated  with  the  definiteness  and  care  that  have 
been  given  to  the  cereals.     The  reason  for  this  has  been  that 
meadow  grasses  occur  abundantly  in  nature,  suitable  both 
for  grazing  and  for  cutting;    and  in  addition  to  this,  plants 
of  other  groups  have  been  found  to  be  extremely  valuable  as 
forage  plants  (that  is,  suitable  for  stock),  as  clover  and  alfalfa. 

3.  Agriculture  and  horticulture.  —  The  cultivation  of  the 
cereals  and  of  the  forage  plants  is  the  work  of  the  farmer,  and 
is  included  in  the  practice   called  agriculture.     This  word 
means    "  field-cultivation,"    and   has   come   to   include   not 
merely  the  field-cultivation  of  food  plants,  but  also  the  culti- 


INTRODUCTION  297 

vation  of  domesticated  animals.  The  work  of  the  farmer, 
therefore,  is  plant  and  animal  cultivation,  and  it  is  the  most 
important  work  in  the  world  on  the  side  of  our  material  needs, 
for  upon  the  results  of  this  work  the  human  population  is 
absolutely  dependent. 

In  addition  to  field  crops,  which  are  generally  referred  to 
under  the  head  of  agriculture,  and  which  are  chiefly  the 
cereals,  there  are  the  so-called  garden  crops,  which  include 
a  great  variety  of  plants.  "  Garden-cultivation  "  is  horti- 
culture, and  it  has  come  to  include  the  cultivation  of  fruits, 
of  vegetables,  and  of  flowers  and  ornamental  plants.  In  a 
broad  sense,  all  cultivation  of  land  for  producing  crops  is 
agriculture,  but  it  is  often  convenient  to  distinguish  among 
the  crops.  For  example,  although  the  cultivation  of  flowers 
and  ornamental  plants  is  usually  included  under  horticulture, 
it  is  often  referred  to  as  floriculture. 

By  whatever  names  the  various  kinds  of  culture  may  be 
called,  the  obvious  fact  is  that  ordinary  plant  culture  deals 
with  five  large  kinds  of  crops :  (1)  cereals,  (2)  forage  plants, 
(3)  vegetables,  (4)  fruits,  and  (5)  flowers  and  ornamental 
plants.  Attention  has  been  called  to  the  fact  that  very 
few  plants  have  been  selected  for  cultivation.  It  was  natural 
for  men  to  begin  with  a  few  plants  when  agriculture  was  just 
starting ;  but  the  descendants  of  these  men  have  not  added 
as  many  to  the  list  as  would  be  expected.  The  wild  plants 
that  might  be  selected  from  number  nearly  150,000  kinds; 
while  the  plants  cultivated  in  any  extensive  way  for  food 
hardly  number  150  kinds.  Either  our  ancestors  were 
remarkably  acute  in  selecting  out  all  of  the  very  useful 
plants,  or  their  descendants  have  failed  to  take  advantage  of 
a  wealth  of  opportunities  all  about  them. 

In  the  cultivation  of  plants,  the  two  things  to  be  considered 
are  the  plant  and  the  soil. 

4.  The  plant.  —  After  the  right  kind  of  plant  has  been 
selected,  one  must  know  what  that  plant  needs ;  not  only 


298  ELEMENTARY  STUDIES  IN  BOTANY 

what  plants  in  general  need,  but  also  what  that  particular 
kind  of  plant  needs.  It  is  also  true  that  the  needs  of  a  plant 
do  not  always  remain  the  same  throughout  its  whole  develop- 
ment. There  are  three  distinct  periods  in  the  history  of 
most  cultivated  plants  which  must  be  recognized.  The  first 
period  includes  germination,  the  starting  of  the  plant,  whether 
from  a  seed,  a  tuber,  or  a  bulb.  The  second  period  includes 
growth,  which  means  the  development  of  a  vigorous  body. 
The  third  period  includes  maturing,  which  means  the  ripening 
of  seeds  and  fruits,  the  proper  development  of  flowers,  etc. 
The  demands  of  the  plant  are  different  at  these  different 
periods.  In  nature,  plants  have  adjusted  themselves  to  the 
changes  of  the  seasons,  so  that  in  general  the  conditions  at 
sowing  time  differ  appropriately  from  the  conditions  at 
harvest  time ;  and  in  general  men  leave  their  cultivated 
plants  in  these  particulars  to  the  chances  of  nature.  But 
in  proportion  as  the  varying  needs  of  these  different  periods 
are  appreciated,  men  will  be  able  often  to  help  the  plants  to 
their  best  development. 

5.  The  soil.  —  In  addition  to  knowing  the  needs  of  the 
plant,  the  cultivator  of  plants  must  know  the  possibilities  of 
the  soil  in  reference  to  plants.  We  are  coming  to  realize  that 
soil  is  a  very  complex  thing  and  that  we  do  not  know  very 
much  about  it  as  yet.  But  men  have  used  it  so  long  in 
cultivating  plants  that  they  have  learned  some  of  the  neces- 
sary things  to  do,  although  they  may  not  be  able  to  explain 
why  they  are  necessary.  That  soil  in  general  is  adjusted 
for  plant  growth  is  evident  because  in  nature  it  is  clothed 
with  vegetation.  But  we  have  learned  that  we  cannot  leave 
our  cultivated  plants  to  an  unworked  soil  and  get  a  respect- 
able crop.  We  must  know  how  to  handle  the  soil  so  that 
it  may  be  adjusted  in  the  best  possible  way  to  the  needs  of 
plants.  In  order  to  adjust  the  soil  we  must  know  what  it 
contributes  to  plants,  where  it  gets  the  materials  to  contribute, 
how  it  presents  the  materials  to  the  plant.  If  we  know  these 


INTRODUCTION  299 

things  and  others  like  them,  we  may  be  able  to  be  of  decided 
help  to  the  plant ;  and  furthermore,  we  may  be  able  to  help 
the  soil  without  abusing  it,  to  use  it  without  diminishing  its 
usefulness. 

It  is  obvious,  therefore,  that  in  the  following  pages  we  must 
consider  the  structure  and  role  and  manipulation  of  the  soil 
so  far  as  plants  are  concerned,  as  well  as  the  needs  of  our 
cultivated  plants  and  how  to  meet  them. 


CHAPTER   II 
WHAT  PLANTS  NEED 

6.  General  statement.  —  Such  plants  as  we  cultivate  may 
be  thought  of  as  living  machines  that  manufacture  food,  that 
grow,  and  that  finally  store  food.     In  general,  it  is  on  account 
of  the  stored  food  that  they  are  cultivated.     If  the  manu- 
facture of  food  is  to  be  carried  on  efficiently,  there  must  be 
favorable  conditions  and  available  materials.     It  is  necessary 
to  discover  what  these  are,  and  also  whether  we  can  be  of 
assistance  in  supplying  them. 

What  may  be  spoken  of  as  the  conspicuous  conditions  for 
successful  plant  work  are  oxygen,  light,  and  heat.  The 
practical  question  is,  therefore,  how  can  we  assist  plants  in 
securing  these  conditions  ? 

7.  Oxygen.  —  In  reference  to  the  oxygen  supply  obtained 
from  the  air,  it  is  evident  that  it  is  abundant  for  the  parts 
above  ground  wherever  plants  are  cultivated.     But  there 
are  living  and  working  parts  of  the  plant  imbedded  in  the 
soil,  and  most  plants  are  started  by  seeds  buried  in  the  soil, 
and  here  the  problem  of  a  free  oxygen  supply  calls  for  our 
help.     If  the  spaces  within  the  soil  are  filled  with  water,  the 
air  is  excluded ;   if  the  soil  is  packed  too  firmly,  the  air  can- 
not circulate ;  or  if  there  is  too  much  clay  in  the  soil,  the  air 
is  not  free  to  move.     All  such  conditions  must  be  remedied 
if  plants  are  to  grow  well.     The  water  must  be  drained  off  ; 
the  soil  must  be  loosened  up ;   the  impervious  clay  must  be 
mixed  with  something  that  will  give  a  looser  texture  to  the 
soil.     One  of  the  most  common  blunders  in  planting  seeds 
when  artificial  watering  is  employed  is  to  use  too  much  water, 
so  that  the  seeds  are  in  a  "  puddle  "  and  the  air  is  excluded. 

300 


WHAT  PLANTS  NEED  301 

8.  Light.  —  When  it  is  said  that  light  is  necessary  for 
plant  work,  this  does  not  mean  that  bright  sunlight  is  neces- 
sary.    Very  ordinary  light  seems  to  be  sufficient,  and  certain 
experiments  indicate  that  very  much  less  light  than  plants 
usually  receive  is  not  injurious.     It  is  evident,  therefore, 
that  cultivated  plants  are  not  likely  to  lack  light.     It  is  not 
so  much  a  question,  however,  of  the  total  amount  of  light 
as  of  the  presence  of  certain  active  rays  of  light  that  plants 
use  in  the  manufacture  of  food.     When  light  passes  through 
smoke,  its  usefulness  to  plants  is  much  diminished,  and  this 
becomes  a  serious  problem  in  the  neighborhood  of  factories, 
and  in  smoke-ridden  towns   and   cities.     When   light   has 
passed  through  foliage,  the  necessary  active  rays  have  dis- 
appeared, so  that  plants  cannot  grow  completely  shaded  by 
other  plants.     This  is  recognized  in  a  general  way  when  the 
scarcity  of  low  vegetation  in  a  dense  forest  is  noted ;  but  even 
the  densest  forest  lets  some  unscreened  light  through,  and  does 
not  form  so  complete  a  shade  as  many  a  cultivated  crop  forms. 
It  is  a  wise  thing,  therefore,  to  see  to  it  that  plants  under 
cultivation  are  not  densely  shaded  by  other  plants. 

9.  Heat.  —  The  favorable  condition  of  temperature  varies 
for  different  plants  and  for  the  different  periods  of  the  same 
plant.     In  general,  a  lower  temperature  is  more  favorable  for 
a  seedling  than  for  a  maturing  plant,  and  this  fact  is  recog- 
nized in  the  spring  sowing  and  summer  harvesting  of  ordinary 
crops,  as  wheat.     The  variation  in  the  temperature  require- 
ments of  different  seedlings  also  explains  why  some  seeds 
are  planted  earlier  in  the  season  than  others.     The  successful 
extension  of  crops  into  different  latitudes  has  depended  upon 
securing  varieties  with  different  temperature  ranges.     The 
results  of  passing  beyond  the  best  temperature  range  in  either 
direction  are  soon  obvious  in  a  plant.     If  the  temperature  is 
too  low,  the  plant  grows  very  slowly;   if  it  is  too  high,  the 
plant  becomes  unusually  tall  and  slender ;  and  in  both  cases 
its  lack  of  vigor  is  shown  by  the  fact  that  it  is  unusually 


302  ELEMENTARY    STUDIES   IN   BOTANY 

subject  to  disease.  In  certain  kinds  of  crops,  these  symp- 
toms suggest  some  kind  of  protection  against  excessive  cold 
or  heat. 

10.  Water.  —  Water  may  be  regarded  not  only  as  a 
necessary  condition  for  plant  work,  but  also  as  a  material 
used  in  the  manufacture  of  plant  food.  The  active  plant 
body  is  really  saturated  with  water,  and  the  living  substance 
(protoplasm)  cannot  work  effectively  unless  it  contains  an 
abundance  of  water.  In  addition  to  the  water  that  puts  a 
plant  in  working  condition,  a  much  smaller  amount  is  used 
in  the  manufacture  of  carbohydrates  (sugar  and  starch)  by 
leaves.  A  saturated  plant  exposed  to  air  means  a  continual 
evaporation  from  its  free  surfaces,  and  notably  from  its 
leaves.  This  loss  must  be  made  good  by  the  continuous 
entrance  of  the  water  of  the  soil  into  the  roots,  so  that  there 
is  a  continual  movement  of  water  through  a  plant.  When  the 
loss  of  water  exceeds  the  supply,  the  immediate  effect  on  the 
plant  is  seen  in  its  "  wilting."  It  is  this  condition  that  all 
plant  cultivation  must  guard  against. 

In  the  case  of  many  field  crops,  there  is  no  control  of  the 
water  supply,  and  the  farmer  must  take  his  chances  that  the 
rainfall  will  be  adequate.  But  in  gardens  it  is  usually  possible 
to  supplement  a  failing  water  supply,  and  in  dry  regions  where 
irrigation  is  used  the  water  supply  is  under  control.  In  all 
cases  where  water  is  supplied  in  some  way  by  the  cultivator, 
it  is  necessary  to  learn  the  needs  of  the  crop.  Generally  too 
much  water  is  supplied,  which  injures  both  the  plant  and  the 
soil.  It  should  be  recognized  also  that  the  amount  of  water 
required  varies  with  the  period  of  the  plant;  for  example, 
more  water  is  needed  during  the  growth  of  the  plant  than 
during  either  seed-germination  or  ripening.  The  problem 
is  not  merely  to  induce  plants  to  grow  by  just  keeping  them 
from  wilting,  but  to  enable  them  to  grow  vigorously.  Too 
little  water  during  the  growing  period  results  in  smaller 
leaves  and  less  work;  while  a  supply  of  water  that  favors 


WHAT  PLANTS   NEED  303 

vigorous  growth,  if  continued  too  long,  will  delay  ripening. 
No  definite  rules  for  watering  can  be  given,  for  it  is  only 
experience  in  observing  the  condition  of  plants  that  can 
suggest  the  amount  of  water  necessary. 

In  determining  what  crops  can  be  grown  to  the  greatest 
advantage  on  a  given  area,  the  supply  of  water  must  be  taken 
into  account.  For  example,  where  there  are  drier  and  wetter 
areas,  wheat  would  be  appropriate  for  the  drier  ground  and 
meadow  grass  for  the  wetter,  and  so  for  each  crop.  The 
ability  to  select  the  most  suitable  plant  for  a  given  area  is  one 
of  the  first  things  a  cultivator  of  plants  must  acquire,  unless 
the  water  supply  is  under  control. 

In  considering  the  other  materials  needed  by  the  plant,  it 
will  not  be  necessary  to  include  all  that  have  been  found  to 
be  used  by  plants,  but  only  those  that  have  proved  to  be  the 
most  important. 

11.  Carbon  dioxide.  — Of  course  carbon  dioxide  must  be 
ranked  with  water  as  of  first  importance,  because  these  two 
materials  are  used  in  the  manufacture  of  carbohydrate  food, 
upon  which  also  depends  the  manufacture  of  other  foods. 
Since  carbon  dioxide  enters  the  plant  from  the  air,  its  supply 
is  usually  sufficient,  and  in  any  event  there  is  nothing  to  do 
in  the  way  of  regulating  the  supply. 

12.  Nitrogen.  —  The  other  materials  needed  by  the  plant 
are  obtained  from  the  soil,  and  with  these  the  practice  of 
agriculture  has  very  much  to  do.     Chief  among  these  ma- 
terials are  the  compounds  of  nitrogen.     Although  nitrogen 
forms  a  very  large  part  of  the  air,  it  cannot  be  used  by  plants 
in  its  free  condition,  but  must  be  obtained  from  its  com- 
pounds.    Of  all  the  compounds  of  nitrogen,  it  appears  that 
the  nitrates  are  most  used  by  plants.     It  is  evident,  there- 
fore, that  nitrates  must  exist  'in  the  soil  if  plants  are  to  be 
grown ;    and  that  if  they  become  insufficient  in  amount, 
they  must  be  restored  in  some  way.     As  in  the  case  of  other 
things  that  plants  need,  the  nitrates  may  be  not  only  insuffi- 


304  ELEMENTARY   STUDIES   IN   BOTANY 

cient  in  amount,  but  they  may  be  excessive  in  amount,  so 
that  too  much  as  well  as  too  little  is  injurious  to  the  crop. 
The  plants  show  the  symptoms  of  both  these  troubles,  lack 
of  nitrates  resulting  in  starved-looking  plants,  and  an 
excess  of  nitrates  resulting  in  weedy-looking  plants  and 
delayed  ripening.  For  example,  with  an  excess  of  nitrates, 
cereals  "  run  to  straw  "  and  ripen  poorly.  Of  course,  if 
rank  growth  rather  than  grain  or  fruit  is  desired,  as  in  the 
case  of  cabbages,  a  larger  amount  of  nitrates  is  helpful. 
This  will  serve  to  illustrate  how  the  use  of  nitrates  will  depend 
upon  the  kind  of  plant,  the  age  of  the  plant,  and  the  product 
desired.  This  means  that  the  successful  cultivator  of  plants 
must  develop  an  experience  in  the  observation  of  his  plants 
that  will  enable  him  to  recognize  their  symptoms. 

In  connection  with  the  problem  of  nitrogen  supply,  it  is 
important  to  know  that  leguminous  plants  have  developed 
an  unusual  method  of  securing  nitrogen.  These  plants 
include  such  crops  as  clover  and  alfalfa.  In  these  cases, 
therefore,  the  problem  of  nitrogen  supply  is  very  different 
from  that  in  non-leguminous  plants.  Such  plants  as  clover 
and  alfalfa  can  draw  upon  the  free  nitrogen  of  the  air,  as  it 
circulates  in  the  soil,  by  means  of  their  association  with 
certain  bacteria  of  the  soil  which  have  the  power  of  "  fixing  " 
free  nitrogen  in  its  compounds.  Leguminous  plants,  there- 
fore, are  very  useful  in  increasing  the  amount  of  nitrates  in 
the  soil ;  while  non-leguminous  plants,  if  removed  as  crops, 
diminish  the  amount  of  nitrates.  This  fact  explains  the 
significance  of  a  very  common  form  of  "  rotation  of  crops," 
for  it  is  obvious  that  the  supply  of  nitrates  in  a  soil  may  be 
kept  sufficient  by  alternating  crops  .of  leguminous  and  non- 
leguminous  plants.  The  clovers  and  alfalfa  are  used  exten- 
sively in  this  way. 

13.  Phosphorus.  — Another  important  group  of  substances 
needed  by  plants  and  supplied  by  the  soil  are  phosphates, 
from  which  the  growing  plants  obtain  such  phosphorus  as 


WHAT   PLANTS  NEED  305 

they  need.  One  of  the  remarkable  effects  of  phosphates 
has  been  shown  to  be  a  greater  ability  to  form  roots,  so  that  in 
soils,  as  clays,  in  which  roots  do  not  develop  readily,  phos- 
phates are  of  great  use.  Phosphates  are  also  said  to  hasten 
the  ripening  processes.  It  should  be  recognized,  however, 
that  fluctuations  in  the  supply  of  phosphates  do  not  show 
such  important  results  in  the  plant  as  fluctuations  in  the 
supply  of  nitrates.  In  fact,  plants  show  decided  symptoms 
of  nitrogen  starvation,  but  there  are  no  recognizable  symp- 
toms of  phosphorus  starvation.  One  of  the  questions  under 
discussion  is  as  to  the  natural  supply  of  phosphates,  some 
maintaining  that  the  phosphates  are  disappearing  from  the 
soil  in  an  alarming  way,  and  others  maintaining  that  the 
supply  is  sufficient  for  an  indefinite  time. 

14.  Other    soil    salts.  —  Numerous   other    salts,    as    the 
compounds  in  the  soil  are  called,  are  needed  by  plants  in  one 
way  or  another,  as  compounds  of  sulphur,  potassium,  cal- 
cium, magnesium,  iron,  etc.     What  these  substances  enable 
the   plant  to   do   is   known  in  some  cases,  but   in  others 
the   particular   use    has   not    been   discovered.     But   they 
are   all  constituents  of  the  soil,  and   have  to  be  reckoned 
with. 

15.  Toxic  substances.  —  It  is  not  only  necessary  to  deter- 
mine whether  a  soil  contains  the  substances  that  plants  need, 
but  also  whether  it  contains  substances  injurious  to  the  plants 
we  wish  to  cultivate.     Such  substances  are  spoken  of  in  a 
general  way  as  toxic  substances.     For  example,  a  soil  may 
contain  too  much  acid  or  too  much  alkali,  and  such  a  soil 
must   be   treated  accordingly,  that   it  may  become  more 
neutral.     Compounds  of  metals  getting  into  the  water  supply 
in  the  waste  products  drained  away  from  industrial  establish- 
ments working  on  metals  may  be  very  injurious  to  cultivated 
plants.     Gases  of  various  kinds  diffused  through  the  air  from 
manufacturing  establishments  may  be  very  destructive  to 
plants,  or  at  least  prevent  vigorous  growth. 


306  ELEMENTARY   STUDIES   IN   BOTANY 

16.  Limiting  factors.  —  It  is  evident  that  in  cultivating 
plants  we  are  not  dealing  with  one  condition  or  one  substance, 
but  with  a  complex  of  conditions  and  substances.  The 
various  conditions  and  substances  may  be  spoken  of  as 
factors  that  have  to  do  with  successful  plant  growth.  We 
have  discussed  six  important  factors  and  have  indicated 
several  more.  It  is  a  very  common  mistake  to  suppose  that 
if  some  one  factor  is  supplied,  plants  will  do  well.  For 
example,  some  will  say  that  a  proper  water  supply  will  insure 
good  plants;  others  will  claim  that  a  supply  of  nitrates  is 
all  that  is  necessary  for  plants  to  do  well ;  still  others  are  just 
as  strenuous  in  reference  to  phosphates  as  the  only  cure  for 
feebleness  in  plants.  In  this  way  a  great  number  of  so-called 
"  fertilizers  "  have  been  devised,  each  claiming  to  supply  all 
plants  whatever  they  need.  It  must  be  evident,  when  it  is  ap- 
preciated that  numerous  factors  in  combination  are  affecting 
the  plant,  that  any  factor  or  even  several  factors  may  be  favor- 
able, and  yet  the  plant  cannot  do  well  if  any  one  necessary 
factor  is  unfavorable.  In  other  words,  a  plant  cannot  do  any 
better  than  the  most  unfavorable  factor  permits,  and  such  a 
factor  is  called  a  limiting  factor.  For  example,  the  necessary 
nitrates  or  phosphates  may  be  supplied,  but  if  the  water 
supply  is  too  scanty  or  too  abundant,  the  water  is  a  limiting 
factor,  and  the  nitrates  or  phosphates  cease  to  be  serviceable. 
In  another  case  the  water  supply  and  the  phosphates  may 
be  just  right,  but  if  the  supply  of  nitrates  is  not  right,  then 
the  nitrates  form  the  limiting  factor  and  impede  the  plant 
in  spite  of  its  favorable  water  and  phosphate  supply.  Any 
one  of  a  half  dozen  or  more  factors,  therefore,  may  be  a 
limiting  factor,  and  it  is  the  limiting  factor  that  determines 
the  success  of  a  plant.  It  is  like  a  group  of  men  walking; 
the  group  as  a  whole  advances  no  more  rapidly  than  the 
slowest  walker.  In  other  words,  the  slowest  walker  is  the 
limiting  factor. 

When  plants  are  not  doing  well,  therefore,  the  course  to 


WHAT  PLANTS  NEED  307 

pursue  is  not  to  apply  some  treatment  that  is  claimed  to  be  a 
cure-all,  but  to  discover,  if  possible,  the  limiting  factor  which 
is  holding  back  the  usefulness  of  the  numerous  factors  that 
are  all  right.  A  plant  that  is  not  doing  its  best  is  like  a 
train  moving  with  brakes  set ;  and  the  thing  to  discover  is  the 
factor  that  is  acting  as  a  brake. 

The  increased  success  of  agriculture  and  of  horticulture 
will  depend  largely  upon  the  development  of  an  ability  to 
recognize  limiting  factors.  The  difference  between  the  old 
agriculture  and  the  new  will  be  the  difference  between  the 
method  of  the  old  medical  practitioner,  with  his  calomel  and 
quinine  for  every  ailment,  and  the  method  of  the  modern 
practitioner,  with  his  developed  powers  of  diagnosis  and  his 
great  variety  of  prescriptions.  It  is  very  important  for  the 
cultivator  of  plants,  at  the  very  outset  of  his  training,  to  pos- 
the  idea  of  limiting  factors. 


CHAPTER   III 
WHAT  THE   SOIL  SUPPLIES 

17.  Chemistry  of  the  soil.  —  The  soil  is  a  mixture  of  many 
substances  that  have  come  from  various  sources.  In  the 
first  place,  its  original  material  and  relatively  permanent 
part  consists  of  material  derived  from  rocks  in  various  ways, 
such  as  particles  of  sand,  clay,  etc.  If  during  its  history  it 
was  submerged  in  sea  water  or  fresh  water,  it  became  mixed 
with  shells  of  water  animals,  which  contributed  calcium  salts 
(carbonates  and  phosphates).  When  it  began  to  be  covered 
with  vegetation  and  the  plants  contributed  their  bodies  to 
the  mixture,  there  was  a  slow  accumulation  of  this  organic 
material  (humus)  which  gave  a  dark  color  to  the  soil  mix- 
ture. To  all  of  these  substances  the  water  of  the  soil  must 
be  added  as  of  great  importance,  containing  in  dilute  solution 
the  substances  of  the  soil  that  are  soluble. 

The  differences  among  soils  are  brought  about  by  the 
various  proportions  in  which  these  substances  occur  in  the 
soil  mixture,  and  it  is  evident  that  the  combinations  are 
numerous.  Soils  are  spoken  of  as  sandy  soils,  clay  soils, 
lime  (calcareous)  soils,  alkali  soils,  acid  soils,  humus  soils, 
etc.,  because  they  are  rich  in  sand,  clay,  lime,  salts,  acids, 
humus,  etc.  Humus  soils,  rich  in  organic  material,  may  be 
too  acid  for  plants  of  ordinary  cultivation  because  there  is 
not  enough  lime  to  neutralize  the  acids  from  decomposition ; 
but  when  there  is  sufficient  lime,  the  humus  is  rendered 
neutral  and  is  very  favorable  for  plants. 

The  effects  of  these  numerous  substances  upon  on'e  another 
are  intricate  and  poorly  understood,  but  enough  is  known 
to  assure  us  that  chemical  changes  are  always  in  progress, 

308 


WHAT   THE    SOIL   SUPPLIES  309 

and  that  the  soil,  in  this  respect,  may  be  regarded  as  a  chem- 
ical laboratory  where  work  is  going  on  continuously. 

18.  Physics  of  the  soil.  —  Not  only  is  the  chemistry  of  the 
soil  necessary  to  consider,  but  the  physical  properties  are  also 
very  important.  This  is  a  subject  of  great  difficulty  on 
account  of  the  complex  mixture.  The  physical  properties  of 
a  mass  of  pure  sand  or  of  pure  clay  may  be  discovered  with 
comparative  ease,  but  when  many  substances,  with  different 
physical  properties,  are  mixed  together,  the  resulting  physical 
properties  of  the  mixture  as  a  whole  form  a  far  more  difficult 
problem.  From  this  point  of  view,  the  soil  may  be  regarded 
also  as  a  physical  laboratory,  which  is  but  dimly  understood. 

A  few  examples  will  illustrate  what  is  meant  by  physical 
properties.  One  of  the  most  important  physical  properties 
of  soil  is  its  relation  to  water.  In  fact,  the  capacity  of  soils 
to  receive  water  and  to  retain  it  in  an  available  condition  for 
plants  is  the  most  obvious  physical  feature  that  cultivation  of 
the  soil  seeks  to  control.  The  clay  constituent  of  a  soil, 
which  is  a  very  important  one,  may  be  taken  as  an  illustration 
of  the  relation  of  one  kind  of  soil  material  to  the  water  supply. 
A  certain  amount  of  clay  interferes  with  the  free  movement 
of  water,  and  therefore  prevents  it  from  draining  away  too 
rapidly;  it  thus  increases  the  retentive  power  of  the  soil. 
But  an  excessive  amount  of  clay  interferes  too  much  with  the 
movement  of  water  and  results  in  a  water-soaked  soil  which 
is  very  injurious  to  plants  on  account  of  the  exclusion  of  air. 
The  converse  is  true  in  reference  to  sand.  A  certain  amount 
of  sand  makes  the  soil  open  to  the  movement  of  water,  thus 
increasing  its  receptive  power ;  but  an  excessive  amount  of 
sand  makes  the  soil  too  open,  so  that  the  water  drains  away 
rapidly  and  the  soil  becomes  dry. 

The  lime  constituents  of  the  soil  are  very  important  both 

chemically  and  physically.     Soils  with  insufficient  lime  are 

spoken  of  in  general  as  "  sour."     Wherever  decomposition 

of  organic  matter  is  going  on,  as  is  true  of  all  good  soils,  there 

21 


310  ELEMENTARY   STUDIES   IN   BOTANY 

is  a  liberation  of  acids,  and  if  these  accumulate,  the  soil 
becomes  literally  sour,  a  condition  which  the  presence  of  lime 
corrects  by  neutralizing  the  acids.  But  lime  is  also  of  great 
value  in  clay  soils  in  a  physical  way,  by  mixing  with  the  clay 
and  making  the  soil  of  better  texture  for  the  handling  of 
water. 

The  humus  (organic  material)  of  the  soil  greatly  increases 
its  water-holding  capacity.  In  fact,  a  forest  soil,  in  general  the 
best  example  of  a  humus  soil,  has  the  physical  properties  of  a 
sponge  in  receiving  and  retaining  water. 

It  becomes  evident  that  in  tfiis  single  matter  of  water  rela- 
tions the  proper  balance  among  the  various  soil  constituents 
is  of  great  importance,  and  that  this  balance  may  be  secured 
in  a  variety  of  ways.  It  should  not  be  forgotten  that 
the  physical  properties  of  the  soil  mixture  in  reference  to 
water  represent  only  one  phase  of  the  physical  properties  of 
soil. 

19.  Life  of  the  soil.  —  The  soil  is  not  only  a  chemical  lab- 
oratory and  a  physical  laboratory,  but  it  is  also  a  biological 
laboratory.  This  means  chiefly  that  it  contains  multitudes  of 
the  exceedingly  minute  plants  called  bacteria.  The  bacteria 
of  the  soil  have  come  to  be  recognized  as  the  most  important 
agents  for  putting  the  soil  in  proper  condition  for  such  plants 
as  we  cultivate.  Bacteria  are  active  in  all  decompositions 
of  organic  material,  which  is  thus  reduced  to  substances  that 
the  plants  can  use.  They  are  active  also  in  many  other  use- 
ful changes  of  soil  material.  Conspicuous  among  their 
activities,  however,  is  their  relation  to  the  nitrogen  supply  of 
the  soil.  Certain  bacteria,  unlike  other  plants,  can  use  the 
free  nitrogen  of  the  air,  and  in  this  use  the  nitrogen  enters 
into  compounds  that  cultivated  plants  can  use.  This  is 
spoken  of  as  the  "  fixation  "  of  nitrogen,  which  simply  means 
taking  free  nitrogen  and  putting  it  into  compounds.  It  is 
evident,  since  plants  must  always  have  a  nitrogen  supply 
from  the  soil,  that  this  work  of  the  nitrogen-fixing  bacteria 


WHAT   THE    SOIL   SUPPLIES  311 

is  of  the  first  importance.  In  removing  crops  the  nitrogen 
compounds  obtained  by  the  plants  from  the  soil  are  removed 
also,  and  if  there  were  no  way  of  restoring  these  compounds, 
the  soil  would  sooner  or  later  become  so  impoverished  in 
them  that  it  could  not  produce  a  good  crop ;  in  other  words, 
it  would  result  in  a  nitrogen  famine. 

Since  the  nitrogen-fixing  bacteria  are  continually  adding 
nitrogen  compounds  to  the  soil,  the  loss  is  represented  by  the 
difference  between  what  the  crops  remove  and  what  the 
bacteria  add.  This  difference  varies  with  the  crop  and  with 
the  soil,  but  in  most  cases  there  is  a  real  loss,  so  that  con- 
tinuous cropping  reduces  the  amount  of  nitrogen  compounds 
to  the  danger  point.  If  a  field  has  become  reduced  to  the 
point  of  a  nitrogen  famine,  it  may  be  restored  to  usefulness 
by  "  resting  "  for  a  time  until  the  bacteria  have  restored  the 
nitrogen  compounds.  This  resting  of  a  field,  that  is,  not 
working  it  for  a  crop,  is  called  letting  a  field  lie  fallow. 

The  restoration  of  nitrogen  compounds  in  this  way,  how- 
ever, is  usually  too  slow  a  process  for  our  purpose.  A  much 
more  rapid  way  is  by  means  of  a  "  rotation  of  crops."  It  is 
found  that  soil  is  kept  in  much  better  condition  as  to  nitrogen 
if  the  same  crop  is  not  grown  continuously  upon  it.  Crops 
vary  as  to  their  wastefulness  of  nitrogen,  so  that  if  a  crop  that 
removes  a  minimum  amount  of  the  nitrogen  compounds 
alternates  with  a  crop  that  removes  a  maximum  amount  of 
these  compounds,  a  nitrogen  balance  may  be  maintained. 
By  far  the  most  effective  rotation  is  secured  by  using  legu- 
minous plants  as  the  alternating  crop,  notably  the  clovers  and 
alfalfa,  for  these  plants  add  nitrogen  compounds  to  the  soil. 
This  peculiar  property  of  leguminous  plants  is  due  to  the  fact 
that  their  roots  become  intimately  associated  with  nitrogen- 
fixing  bacteria  which  inhabit  tubercles  (little  tubers)  that 
form  on  the  roots,  and  in  these  tubercles  there  is  an  accumu- 
lation of  nitrogen  compounds  not  obtained  from  the  nitrogen 
compounds  of  the  soil,  but  produced  by  the  bacteria  in  using 


312  ELEMENTARY   STUDIES   IN   BOTANY 

the  free  nitrogen  of  the  air.  Such  plants,  therefore,  not  only 
do  not  draw  upon  the  nitrogen  supply  of  the  soil,  but  they  are 
the  means  of  adding  to  it. 

20.  The  soil  complex.  —  The  above  paragraphs  give  only 
a  glimpse  of  the  complexity  of  the  soil,  with  its  chemical  con- 
stituents, its  physical  properties,  and  its  active  bacterial  life. 
It  is  a  great  complex  in  which  changes  are  always  taking 
place,  and  which  can  be  thrown  out  of  balance  in  a  number 
of  ways.     Left  to  itself  and  to  natural  vegetation,  it  becomes 
better  for  plants  with  each  succeeding  year ;    but  interfered 
with  by  man,  who  rarely  appreciates  what  he  is  doing,  it 
frequently  gets  into  bad  condition.     This  is  notably  true 
when  attempts  are  made  to  remedy  unknown  troubles  by 
"  fertilizing  "  with  unknown  substances,  especially  with  the 
so-called  "  chemical  fertilizers,"  which  are  as  dangerous  to 
the  soil  in  the  hands  of  inexperienced  people  as  are  strong 
medicines  in  the  hands  of  the  untrained.     While  destroying 
the  chemical  or  physical  equilibrium  of  a  properly  balanced 
soil  is  bad  enough,  any  interference  with  the  bacterial  life  of 
the  soil  is  worse.     These  statements  merely  serve  to  empha- 
size the  fact  that  any  efficient  manipulation  of  the  soil, 
especially  in  adding  materials  to  it,  requires  experience  and 
considerable  knowledge. 

21.  Tillage.  —  The  preceding  paragraphs  have  outlined  in 
a  general  way  what  the  soil  supplies  to  plants  we  cultivate. 
It  is  well  known,  however,  that  all  the  appropriate  materials 
may  be  present,  and  yet  the  soil  must  be  "  worked  "  for  plant- 
ing seeds  and  also  to  help  the  growing  plants.     This  "  work- 
ing "  of  the  soil  is  called  tillage,  and  its  purpose  is  to  put  the 
soil  into  the  best  possible  physical  condition.     Tillage  of  the 
soil  is  the  first  and  principal  thing,  and  often  the  only  neces- 
sary thing.     If  any  "  fertilizers  "  are  to  be  added,  this  is  a 
iratter  of  secondary  importance.     In  fact,  there  is  much 
experience  to  show  that  proper  tillage  reduces  and  often 
eliminates  the  need  for  fertilizers.     Of  course  proper  tillage 


WHAT   THE    SOIL   SUPPLIES  313 

is  laborious,  and  fertilizers  are  often  used  as  short  cuts  to 
save  labor. 

The  breaking  up  of  the  soil  for  planting  seeds  is  known 
to  every  one,  but  its  purpose  is  not  so  widely  understood. 
Many  suppose  that  it  is  only  a  way  of  getting  seeds  into  the 
ground,  but  that  is  the  least  important  of  its  purposes.  Its 
real  purpose  is  to  pulverize  the  soil,  because  finely  pulverized 
soil  is  in  the  best  physical  condition  for  plants.  In  the  first 
place,  it  secures  a  good  circulation  of  air,  which  we  have 
learned  is  essential  for  the  best  plant  growth.  In  the  second 
place,  it  enables  the  soil  to  hold  a  much  larger  amount  of 
moisture.  Strange  as  it  may  seem  at  first  thought,  the 
smaller  the  soil  particles  and  the  closer  together  they  are, 
the  more  water  will  the  soil  hold.  This  is  explained  by  the 
fact  that  the  amount  of  water  held  by  the  particles  is  approxi- 
mately in  proportion  to  the  surface  they  present,  and  of 
course  there  is  much  more  surface  presented  by  very  numer- 
ous small  particles  in  a  given  space  than  by  less  numerous 
large  particles.  The  capacity  of  a  soil  for  water,  therefore, 
is  in  proportion  to  the  minuteness  of  its  particles.  This  com- 
bination of  small  particles  and  free  circulation  of  air  is  an 
ideal  combination  for  productive  soil.  Of  course,  pulverizing 
the  soil  also  improves  its  drainage,  and  so  permits  unimpeded 
circulation  of  air. 

The  ideal  physical  condition  of  the  soil  is  attained  in  the 
potting  of  plants,  in  which  the  soil  is  pulverized  and  screened, 
but  this  degree  of  tillage  is  not  practicable  when  large  areas 
are  concerned.  And  still  it  shows  that  the  more  persistent 
and  painstaking  the  tillage,  the  better  the  results  in  crops. 

After  the  soil  is  well  tilled,  and  the  seeds  are  sown,  the  work 
of  tillage  is  not  at  an  end.  The  physical  conditions  that  favor 
germinating  seeds  also  favor  growing  plants;  therefore  the 
soil  must  be  kept  in  good  physical  condition.  An  additional 
advantage  of  tillage  to  growing  plants  must  be  mentioned, 
and  that  is  the  conservation  of  moisture.  Water  not  only 


314  ELEMENTARY   STUDIES   IN    BOTANY 

drains  away  from  the  soil,  retained  more  or  less  by  a  finely 
pulverized  soil,  but  it  also  evaporates  from  the  surface.  If 
the  surface  becomes  caked,  it  must  be  broken  up  and  pul- 
verized so  that  the  soil  can  get  a  new  grip  on  the  water,  or 
the  loss  may  be  serious.  Tillage,  therefore,  checks  evapora- 
tion as  well  as  loss  by  drainage.  In  fact,  in  dry  farming  it 
has  been  found  that  a  shallow  pulverized  layer  of  soil  acts 
like  a  "  mulch  "  or  a  blanket  in  checking  evaporation.  Of 
course  it  is  common  to  use  an  artificial  "  mulch  "  for  the 
same  purpose,  such  as  a  layer  of  ashes  or  sawdust  or  leaves ; 
but  shallow  tillage  provides  a  natural  mulch. 

22.  Capillary  movement  of  water.  —  It  must  not  be 
thought  that  the  only  water  available  for  plants  is  that  which 
is  held  by  the  soil  particles  with  which  their  roots  come  in 
contact.  A  most  important  fact  is  the  capillarity  of  the  soil. 
This  means  that  when  films  of  water  held  by  the  soil  particles 
become  thinner  because  some  of  the  water  has  entered  the 
roots,  there  is  a  rearrangement  of  the  water  in  all  the  neigh- 
boring films.  Water  is  always  pulled  away  from  a  thicker 
film  toward  a  thinner  one,  and  this  starts  a  movement  of 
water  from  every  direction  towards  the  thinner  films.  There- 
fore, as  water  is  lost  from  the  soil  by  evaporation  or  by  pass- 
ing into  root  systems,  there  is  a  movement  of  water  from  the 
deeper  parts  of  the  soil.  This  is  the  so-called  capillary 
movement  of  water,  which  is  in  the  main  an  ascending  move- 
ment. The  available  water  for  plants,  therefore,  is  all  the 
water  in  the  neighborhood  that  is  free  to  move  through  the 
soil.  If  the  soil  is  in  proper  condition,  this  capillary  move- 
ment extends  to  the  water-table,  which  means  the  level  where 
the  ground  begins  to  be  saturated  with  water,  usually  because 
it  is  held  by  some  material  through  which  it  cannot  pass. 
This  impervious  material  may  be  clay  or  rock.  For  this 
reason,  not  only  is  the  soil  in  which  the  plants  are  rooted  to 
be  considered,  but  also  the  soil  beneath,  which  is  called  the 
subsoil.  For  example,  it.  is  of  great  advantage  to  an  open 


WHAT   THE    SOIL   SUPPLIES  315 

sandy  soil  to  rest  upon  a  subsoil  of  clay,  which  holds  a  body  of 
water  within  reach  of  the  soil  above.  Without  such  a  sub- 
soil a  sandy  soil  would  be  in  danger  of  becoming  too  dry. 

,23.  Movement  of  soil  salts.  —  It  is  a  very  common  mis- 
take to  suppose  that  the  only  soil  salts  available  for  plants 
are  those  with  which  the  roots  come  in  contact.  For  this 
reason,  the  different  useful  salts  occurring  in  what  is  called 
"  plough  depth  "  of  soil  (6  to  9  inches)  have  been  estimated, 
and  the  conclusion  reached  that  when  this  amount  of  any 
necessary  salt  has  been  used  up,  the  soil  will  be  impoverished. 
What  has  been  said  concerning  the  capillary  movement  of 
water  through  the  soil  should  correct  this  impression.  The 
moving  water  contains  the  useful  salts  in  solution,  and  there- 
fore the  salts  are  also  moving  towards  the  surface  continually. 
It  must  be  remembered  that  this  movement  is  not  only 
towards  the  points  where  the  water  and  salts  are  entering  the 
plants,  but  also  towards  the  general  surface  from  which  the 
water  is  being  evaporated.  Quite  apart  from  the  use  of  salts 
by  plants,  therefore,  they  are  continually  moving  towards 
the  surface  in  solution  and  being  deposited  in  the  surface 
layers  by  the  evaporation  of  the  water. 

This  means  that  the  salt  available  for  plants  is  not  only 
that  which  happens  to  be  within  the  surface  soil  at  a  given 
time,  but  also  all  that  is  within  reach  of  the  water  movement. 
This  usually  multiplies  many  times  the  amount  in  the  surface 
soil,  for  the  movement  of  water  may  extend  to  a  great  depth, 
and  when  it  reaches  the  underlying  rocks,  the  supply  of 
certain  salts  may  be  indefinite. 

24.  Soil  analysis.  —  There  is  a  general  impression  that  if  a 
sample  of  soil  be  sent  to  a  chemist  to  analyze,  he  can  dis- 
cover what  it  lacks  and  prescribe  a  suitable  fertilizer.  This 
kind  of  work  is  sometimes  provided  for  upon  an  extensive 
scale.  If  the  statements  of  the  preceding  paragraphs  are 
true,  it  is  evident  that  no  such  chemical  analysis  can  tell  what 
the  soil  of  any  farm  needs.  In  the  first  place,  the  appropriate 


316  ELEMENTARY   STUDIES   IN    BOTANY 

materials  are  found  in  all  soils  upon  which  natural  vegetation 
can  grow.  Soil  is  a  variable  mixture,  and  there  is  no  fixed 
standard  that  determines  the  best  mixture.  In  the  second 
place,  the  immediate  need  of  any  soil  is  to  be  put  in  proper 
physical  condition,  and  what  is  necessary  to  accomplish  this 
can  be  told  only  by  an  examination  of  the  area ;  it  certainly 
cannot  be  told  from  a  sample. 


CHAPTER  IV 


SEEDS 

25.  Seed  structure.  — It  will  be  well  to  recall  just  wrhat 
a  seed  is  and  what  it  needs  for  germination.  It  is  made  up  of 
three  things  that  must  be  considered :  (1)  the  hard  covering 
(testa),  (2)  the  young  plant  (embryo),  and  (3)  the  food  supply 
(Fig.  1). 

Testa.  —  Seeds  differ  in  the  hardness  and  thickness  of  the 
covering,  and  also  in  its  permeability.  Two  things  must 
pass  through  the  seed  coat  before  germination  can  begin, 
namely  water  and  air  (it  is  the  oxygen  of  the  air  that  is 
needed) .  Some  seed  coats 
are  impervious  to  water, 
others  to  air,  and  others 
to  both,  and  in  nature 
they  may  lie  in  the  soil 
for  a  long  time  before 
germination  begins,  await- 
ing changes  in  the  testa, 
through  decay  or  other- 
wise, .  that  will  permit  the 
entrance  of  water  or  oxy- 
gen or  both.  For  example, 
the  testa  of  the  seeds  of  let- 
tuce is  so  impervious  that 

the  seeds  are  often  stored  for  two  or  three  years  before  being 
sold  for  planting,  and  throughout  this  period  the  germinating 
power  is  probably  diminishing.  On  the  other  hand,  peas  and 
beans  and  corn  germinate  with  great  promptness.  Me- 
chanical means  are  being  devised  to  remove  the  obstruction 

317 


FIG.  1.  —  Seed  of  a  violet :  the  right  figure 
shows  the  hard  seed  coat  (testa)  ;  the  left 
figure  is  a  section,  showing  the  embryo  sur- 
rounded by  the  food  supply  (endosperm), 
which  in  turn  is  surrounded  by  the  testa.  — 
After  BAILLON. 


318 


ELEMENTARY   STUDIES   IN   BOTANY 


to  water  and  oxygen  offered  by  the  testa,  and  in  the  case  of 
many  seeds  this  will  make  a  great  difference  in  the  prompt- 
ness of  germination. 

Embryo.  —  The  young  plant  enclosed  in  the  seed,  often 
called  "  the  germ,"  is  the  structure  that  is  to  work  and  grow 
and  escape  from  the  testa.  The  living  substance  (proto- 
plasm) of  the  embryo  is  in  a  dormant  stage,  which  means  that 
it  is  inactive ;  and  it  needs  the  water  to  put  it  in  a  proper 
condition  for  activity.  As  a  general  rule,  the  longer  dor- 
mancy is  continued,  the  less  active  the  embryo  is  when 
aroused.  The  germinating  power  of  a  seed  is  called  its 
viability,  and  viability  diminishes  as  dormancy  is  prolonged. 
This  is  not  true  for  all  seeds,  for  in  certain  cases  changes 
are  necessary  in  the  embryo  itself  during  dormancy  before 
germination  can  begin.  In  these  cases,  therefore,  viability 
increases  as  long  as  these  changes  in  the  embryo  are  occurring, 
but  after  the  embryo  has  "  ripened," 
the  viability  diminishes  as  germination 
is  postponed. 

It  is  evident  that  the  testa  and  the 
embryo  of  the  plants  we  cultivate  must 
be  better  understood  before  we  can 
secure  in  every  case  prompt  germina- 
tion at  the  time  of  greatest  viability. 

Food  supply.  —  In  many  seeds,  as  in 
the  cereals,  the  food  supply  is  packed 
around  the  embryo  (Fig.  1),  or  at  one 
side  of  it,  as  in  corn  (Fig.  2),  forming 
a  distinct  region  of  the  seed,  called  the 
endosperm.  In  other  seeds,  as  peas  and 
beans,  the  endosperm  has  been  used  up 
by  the  growing  embryo,  and  the  food 
substances  have  been  redeposited  in  the  seed-leaves  (cotyle- 
dons) of  the  embryo,  which  become  large  and  fleshy.  In  this 
latter  case  the  embryo  occupies  all  the  space  within  the  testa 


FIG.  2.  —  Section  of  a  grain 
of  corn,  showing  the  endo- 
sperm at  one  side  of  the 
embryo :  fuller  explana- 
tion in  text  on  p.  349.  — 
After  FRANK. 


SEEDS  319 

(Fig.  3) .  It  is  upon  this  food  material,  whether  stored  in  the 
endosperm  or  in  the  embryo,  that  the  young  plant  must  live 
until  it  establishes  soil  connections  and  exposes  green  leaves 
to  the  light  and  air.  It  is  this  period  of  dependence  upon 
stored  food  that  is  called  germination. 

26.  Seed  selection.  —  The  proper  handling  of  seeds  is  no 
less  important  than  the  proper  tilling  of  the  soil.  The  char- 
acter of  seeds  must  be  investigated  before  planting,  for  the 
character  of  the  crop  will  depend  upon  a  proper  seed  selection. 


FIG.  3.  —  Section  of  bean,  showing  the  embryo  (chiefly  the  fleshy  cotyledons)  filling 
all  the  space  within  the  testa. 

Not  very  many  years  ago  it  was  thought  that  any  kind  of 
seed  is  good  enough  to  plant,  and  so  in  the  case  of  cereals 
the  best  seeds  were  used  for  food,  and  the  poorer  seeds  were 
saved  for  planting.  In  the  case  of  plants  whose  seeds  are 
not  used  for  food,  no  attention  was  paid  to  the  character  of 
the  plant  whose  seeds  were  used  for  planting. 

It  is  now  recognized,  however,  that  seed  selection  is  of  the 
very  first  importance.  A  seed  produces  a  plant  that  very 
closely  resembles  the  parent  plant,  and  if  the  parent  plant  is 
a  poor  specimen  and  has  produced  poor  seed,  its  progeny 
cannot  be  expected  to  do  any  better.  So  important  is  seed 
selection,  therefore,  that  it  has  developed  a  great  industry, 
and  the  business  of  seed  firms  is  to  select  seed,  to  improve  it 


320  ELEMENTARY    STUDIES   IN   BOTANY 

as  much  as  possible,  and  to  multiply  it  in  sufficient  quantity 
to  supply  all  who  need  it.  In  this  way,  those  who  wish  seeds 
can  get  good  ones  to  start  with  from  reliable  seed  firms,  but 
they  should  be  able  to  select  seeds  from  their  own  crops  for 
subsequent  crops. 

In  doing  so,  they  must  select  a  few  plants  that  seem  to  be 
most  desirable.  Of  course  the  standard  of  selection  may 
vary ;  selection  may  be  made  for  some  quality,  for  yield,  for 
appearance,  etc. ;  but  whatever  it  is,  the  plants  selected 
must  be  those  that  come  nearest  to  this  standard.  The 
seeds  from  these  selected  plants  must  be  saved  for  sowing,  and 
the  next  crop  is  likely  to  be  a  little  better  than  the  former  one. 
If  this  careful  selection  is  continued  through  a  series  of  sea- 
sons, the  successive  crops  will  maintain  their  desired  character 
and  will  probably  improve. 

In  the  case  of  corn,  it  has  been  found  that  after  the  selection 
of  good  plants,  the  most  desirable  ears  must  be  selected.  Of 
course  this  selection  means  the  best  ears  from  the  best  plants. 
This  ear-by-ear  selection  in  the  case  of  corn  is  based  upon  the 
fact  that  all  the  grains  of  an  ear  of  corn  are  remarkably  uni- 
form in  character.  This  selection  of  seed  corn,  and  its 
importance  in  the  resulting  crop,  is  being  emphasized  by  the 
formation  of  "  corn  clubs  "  for  boys  in  agricultural  com- 
munities, and  by  contests  between  clubs.  The  United  States 
Department  of  Agriculture  is  so  much  interested  in  such  clubs 
that  it  issues  bulletins  for  them  and  their  contests,  and  has  a 
specialist  in  charge  of  club  work.  These  bulletins  may  be 
obtained  for  the  asking. 

27.  Seed-germination.  —  After  seeds  have  been  selected 
from  desirable  parent  plants,  the  question  of  their  germinating 
power  (viability)  is  an  important  one.  In  general,  this 
germinating  power  is  greatest  in  the  next  season  after  the 
seed  is  produced,  which  of  course  is  the  usual  period  in  nature 
between  seed-production  and  seed-germination.  This  implies 
that  in  general  the  germinating  power  of  a  seed  diminishes 


SEEDS  321 

as  it  becomes  older,  until  finally  it  cannot  be  made  to  germi- 
nate. This  is  a  good  general  rule,  but  like  all  rules  it  has  its 
exceptions.  Failure  to  germinate  at  all  plainly  indicates 
poor  seed  ;  but  unusually  slow  germination  or  feeble  seedlings 
indicate  declining  power  and  relatively  poor  seed.  Seeds 
may  "  sprout,"  that  is,  the  enclosed  plantlet  may  break  the 
seed  coat  and  begin  to  emerge  (Fig.  5),  but  sprouting  is  not 
a  complete  test,  for  there  may  not  be  power  enough  to  carry 
the  germination  to  its  completion,  that  is,  until  the  young 
plant  has  established  itself  in  the  soil  and  has  spread  out  its 
first  leaves.  It  is  important,  therefore,  to  test  the  germinat- 
ing power  of  samples  taken  from  any  lot  of  seeds  obtained  for 
planting. 

The  germinating  power  of  seeds  is  tested  in  a  variety  of  ways, 
sometimes  with  great  exactness,  requiring  considerable 
apparatus  to  control  the  conditions;  at  other  times  with 
varying  degrees  of  exactness,  down  to  germination  between 
two  sheets  of  moist  blotting  paper.  Since  germination  experi- 
ments can  be  conducted  by  any  student,  and  with  little 
or  no  apparatus,  and  since  they  are  so  fundamental  in  the 
cultivation  of  plants,  as  many  experiments  should  be  per- 
formed as  the  time  will  permit.  In  this  case  some  of  the 
simpler  methods  may  be  used. 
A  very  effective  seed-germinator 
for  class  use  is  constructed  as 
follows  (Fig.  4) :  the  bottom  of 
a  flat  tin  basin  (like  a  milk  pan), 
painted  outside  and  inside  to 

prevent    rusting,    is    COVered  With     FlG.  4.  -  A  simple  seed-germinator : 

water,    and    in   it  is  placed  the       explained  in  the  text.  —  After 

BAILEY. 

saucer  of  a  small  flower  pot.     In 

the  bottom  of  the  saucer  a  layer  of  moist  blotting  paper  is 
placed  ;  on  it  are  laid  the  seeds  to  be  germinated ;  and  on  the 
seeds  another  layer  of  blotting  paper  is  placed.  A  pane  of  glass 
is  used  as  a  cover  for  the  pan,  and  the  apparatus  is  complete. 


322 


ELEMENTARY    STUDIES   IN   BOTANY 


It  will  be  necessary  to  leave  the  pan  partly  open  now  and  then 
to  allow  gas  exchanges.  The  principles  of  this  simple  piece 
of  apparatus  may  be  used  with  a  variety  of  details ;  as,  for 
example,  the  substitution  of  two  soup  plates,  one  used  as  a 
cover,  for  the  tin  pan  and  the  pane  of  glass  (Fig.  4a) .  Of  course 
the  most  complete  test  of  the  germinating  power  of  seeds  is 
obtained  by  planting  in  soil  in  conditions  they  must  meet 

when  sown  for  a  crop.  It 
should  be  known  that  seeds 
usually  germinate  much  bet- 
ter in  the  ordinary  germina- 
tion tests  than  they  do  when 
actually  put  in  the  ground 
out  of  doors,  so  that  one 
must  not  expect  that  the 
actual  germination  will 
equal  the  experimental  ger- 
mination. 

The  length  of  time  neces- 
sary for  germination  varies 
widely  with  different  seeds, 
and  these  periods  should  be 
learned  for  plants  that  one 
cultivates.  As  a  rule,  the 
period  of  germination  is 
somewhat  longer  in  soil  than  in  the  ordinary  testing  experi- 
ments in  artificial  conditions.  As  has  been  stated,  some 
seeds  have  such  a  hard  and  bony  covering  that  germina- 
tion may  be  very  much  delayed,  and  in  nature  such  seeds 
may  lie  for  a  season  or  two  or  even  many  seasons  before 
germination  occurs.  It  is  evident  that  any  treatment  of 
seeds  that  will  hasten  germination  is  of  advantage,  but  many 
suggested  treatments  have  been  disapproved  for  most  seeds, 
as  soaking  in  water  or  in  certain  chemicals  before  planting. 
It  has  been  found,  however,  that  any  mechanical  method  of 


FIG.  4a.  —  A  seed-germinator  constructed 
by  using  home  utensils,  as  soup  plates 
or  basins :  in  the  upper  figure  the  ger- 
minator  is  closed ;  in  the  lower  figure 
it  is  open,  showing  the  sheets  of  moist 
blotting  paper  (kept  moist  by  water  in 
the  plate)  between  which  the  seeds  are 
placed.  —  After  WESTGATE. 


SEEDS 


323 


thinning  or  puncturing  or  breaking  the  hard  seed  coat,  with- 
out injuring  the  young  plant  (embryo),  usually  secures 
prompt  germination.  The  whole  subject  of  delayed  germi- 
nation is  under  investigation,  and  it  is  evident  that  it  is  a 
practical  question  of  great  importance.  Experiments  with 
different  seeds  should  be  performed  to  discover  the  ordinary 
variations  in  the  ger- 
minating period. 

The  germination  of 
beans,  which  is  rapid, 
may  be  used  as  a  pre- 
liminary experiment. 
Figs.  5-9  show  some 
of  the  stages.  In  Fig. 
5,  the  tip  of  the  hy- 
pocotyl  has  broken 
through  the  testa ;  in 
other  words,  the  bean 
has  "  sprouted."  In 
Fig.  6,  the  hypocotyl 
is  curving  towards  the 
earth ;  in  Fig.  7,  it 
has  elongated  consid- 
erably; in  Fig.  8,  it 
has  penetrated  the 
earth  and  put  out 
rootlets,  developing  a  sharp  arch.  In  Fig.  9,  the  root  sys- 
tem has  gripped  the  soil,  the  cotyledons  have  been  pulled 
out  of  the  testa,  the  arch  has  straightened,  the  young  stem 
bud  (plumule)  is  seen  between  the  cotyledons,  and  the  seed- 
ling has  established  itself  for  independent  work. 

28.  Depth  of  planting.  —  There  is  no  definite  depth  at 
which  seeds  should  be  planted,  for  it  varies  with  the  condi- 
tions. The  thing  to  remember  is  that  seeds  should  have 
continuous  moisture  in  a  well-tilled  soil.  When  seeds  are 


FIGS.  5-8. — A  germinating  bean :  explained  in  the  text. 


324 


ELEMENTARY    STUDIES   IN   BOTANY 


planted  in  soil  in  pots  or  boxes,  where  the 
water  supply  is  controlled,  they  may  be 
more  shallow  than  if  planted  in  the  open, 
where  the  surface  soil  is  in  danger  of  be- 
cbming  too  dry.  It  is  well  to  plant  seeds 
as  shallow  as  possible,  consistent  with  a 
moist  soil.  Attention  has  been  called  to 
the  fact  that  a  moist  soil  does  not  mean 
one  saturated  with  water,  which  is  a  com- 
mon mistake  made  in  planting  seeds, 
called  very  properly  "  puddling  "  seeds. 
The  danger  involved  in  preventing  a  free 
circulation  of  air  by  filling  the  soil  spaces 
with  water  has  been  mentioned.  Of  course 
the  soil  is  saturated  with  water  after  an 
abundant  rain,  but  if  there  is  proper 
drainage,  this  is  a  very  temporary  blockade 
to  the  air.  The  advantage  of  the  rain,  of 
course,  is  that  in  passing  through  the  finely 

FIG.    9.  —  A    seedling      ,.    .  ,     -i         •  1,1  ,1-1  ji 

bean  just  as  germi-  divided  soil  the  water  thickens  the  water 
films  held  about  the  soil  particles,  and  adds 
to  the  supply  of  water  in  the  deeper  region 
of  the  soil  which  can  be 
drawn  upon  by  the  capil- 
lary movement. 

29.  Seed  boxes.  —  In 
cultivating  many  gar- 
den plants  (including, 
of  course,  flowers  and 
ornamental  plants)  it  is 
often  of  great  advantage 
to  germinate  the  seeds 
in  shallow  boxes  con- 
taining soil,  such  seed 
boxes  as  professional 


the  text. 


FlG.  10._Agardener>sseedboxforgerminating 

seeds.  —  After  BAILEY. 


SEEDS  325 

gardeners  use  (Fig.  10).  In  this  case  such  germinating  con- 
ditions as  water  and  temperature  can  be  controlled,  so  that 
the  accidents  of  dryness  and  chill  can  be  avoided  at  a  very 
critical  period.  In  this  way  germination  is  also  more  prompt 
than  in  the  ordinary  conditions  out  of  doors,  so  that  the 
young  plants  get  started  earlier.  Another  very  important 
advantage  is  that  the  poor  seedlings  can  be  discovered  and 
discarded,  and  only  the  vigorous,  promising  ones  used  in  the 
permanent  bed.  This  enables  one  to  supplement  seed  selec- 
tion by  seedling  selection,  and  the  result  is  a  good,  clean, 
uniform  crop. 

The  transplanting  of  the  selected  seedlings  into  properly 
prepared  permanent  beds  is  a  simple  performance  which 
a  little  practice  will  make  rapid  and  effective.  The  only 
suggestion  needed  is  that  the  rootlets  of  the  seedling  should 
be  disturbed  in  their  soil  connections  as  little  as  possible,  and 
so  with  each  seedling  there  should  also  be  transplanted  a  little 
of  the  soil  in  which  its  root  is  imbedded.  Of  course  seedlings 
may  be  pulled  out  of  the  soil  and  transplanted,  but  time  is 
lost  in  their  recovery  from  this  rough  treatment. 


CHAPTER   V 
OTHER  METHODS  OF  PROPAGATION 

30.  Vegetative  propagation.  —  Plants  can  be  propagated 
in  other  ways  than  by  their  seeds,  and  advantage  is  often  taken 
of  this  fact.     Among  the   advantages   secured   are  a  more 
rapid  production  of  plants  and  a  greater  certainty  that  the 
plants  will  come  true  to  type.     The  greater  rapidity  of  pro- 
duction is  secured  by  eliminating  the  germination  and  seed- 
ling stages,   and  starting  with   considerable  maturity.     In 
the  case  of  plants  of  long  periods,  as  shrubs  and  trees,  this 
shortening  of  the  period  between  the  start  and  the  crop  is  of 
great   importance.     Greater   certainty   as  to  the   character 
of  the  plants  produced  arises  from  the  fact  that  a  seed  has 
come  from  the  act  of  fertilization,  and  this  usually  involves 
the  characters  of  two  parents;    while  the  other  methods  of 
propagation  involve  the  vegetative  continuance  of  one  indi- 
vidual.    For  example,  no  one  thinks  of  raising  potatoes  from 
seeds  to  secure  a  crop.     By  using  the  tubers  (thickened  under- 
ground stems),  new  potato  plants  are  secured  much  more 
speedily,  and  the  new  tubers  are  like  the  parent  tuber.     In 
addition  to  seed  propagation,  therefore,  it  is  necessary  to 
consider   vegetative   propagation.     The   principal   kinds   of 
vegetative  propagation  may  be  included  under  three  heads : 
(1)  cuttings,  (2)  layering,  (3)  grafting. 

31.  Cuttings.  —  By  this  is  meant  that  cuttings  or  "  slips," 
usually  of  the  stem,  can  be  used  to  produce  new  plants.     A 
stem  is  made  up  of  nodes  (joints)  and  internodes  (the  parts 
of  the  stem  between  the  nodes).     The  nodes  have  the  power 
to  produce  lateral  members,  which  ordinarily  are  leaves  and 
branches ;   but  when  nodes  are  put  in  the  proper  soil  condi- 

326 


OTHER   METHODS   OF   PROPAGATION 


327 


tions,  they  can  produce  roots,  also.  Therefore,  if  a  node  puts 
out  a  branch,  which  is  merely  a  new  stem,  and  at  the  same 
time  strikes  root,  a  new  and  independent  plant  is  started. 
It  is  evident,  therefore,  that  propagation  by  cuttings  is 
secured  by  planting  nodes,  and  that  a  good  vigorous  node 
should  be  able  to  produce  a  new  plant,  which  is  a  vegetative 
continuation  of  the  old  plant.  Not  only  are  cuttings  of 
stems  used  for  propagation,  but  also  in  some  cases  cuttings 
of  roots  and  leaves. 

It  must  be  understood  that  propagation  by  cuttings  is  not 
used  with  all  cultivated  plants,  and  it  is  not  known  how  many 
of  them  could  be  propagated  in  this  way.  Some  of  the  more 
important  plants  propagated  by  cuttings  and  the  general 
method  of  procedure  may  be  indicated  by  a  few  illustrations. 
The  details  differ  more  or  less  for  each  kind  of  plant  propa- 
gated in  this  way,  and 
facility  in  this  work  can 
only  be  secured  by  learn- 
ing what  is  necessary  in 
each  case  and  by  practice. 

A  conspicuous  illustra- 
tion of  the  use  of  stem 
cuttings  is  in  the  propaga- 
tion of  grapes.  In  this 
case  the  stems  of  the  cur- 
rent year  are  secured  late 
in  the  season,  before  severe 
cold,  and  either  stored  or 
made  into  cuttings  at 
once.  When  either  stems 
or  cuttings  are  stored,  they  must  be  kept  in  a  cool  place 
and  prevented  from  drying  out  by  some  such  covering  as 
fresh  moss  or  earth.  The  usual  practice  in  making  the 
cuttings  is  to  include  at  least  two  nodes  (indicated  by  buds), 
the  cutting  thus  being  six  inches  or  more  long,  the  upper  cut 


M^?f^^': 


FIG.  11.  —  A  cutting  in  position  in  a  trench. 
—  After  BAILEY. 


328  ELEMENTARY    STUDIES   IN   BOTANY 

being  just  above  the  upper  bud.  In  the  spring,  the  cuttings 
are  planted  "  right  end  up,"  in  well-tilled  soil,  so  that  the 
upper  bud  is  at  the  surface.  The  cuttings  are  not  planted  by 
being  thrust  into  the  soil,  but  are  placed  about  a  foot  apart  in 
trenches  and  covered  up  (Fig.  11).  If  the  cuttings  and  the 
soil  and  the  planting  are  all  what  they  should  be,  many  of  the 
cuttings  will  establish  plants  during  a  single  season,  which 
are  then  ready  for  transplanting  into  a  permanent  position. 

These  details  will  vary  with  different  plants,  largely  depen- 
dent on  the  use  of  young  wood  or  mature  wood  for  cuttings, 
or  on  the  use  of  short  or  long  cuttings.  In  the  grape  cuttings 

just  described, 
the  cuttings 
are  long  and 
contain  ma- 
ture wood. 

The  best  il- 
lustration of 
the  use  of  cut- 


FIG.    12.  —  Potato   tuber,  showing  the  "eyes"  which   indicate    ^jftfrg  Q£ 
nodes,  and  also  some  young  branches  ("sprouts")  started. 

ground    stems 

is  in  the  propagation  of  potatoes.  The  potato  tubers  are 
thickened  underground  stems,  and  their  nodes  have  all  the 
powers  of  those  of  aerial  stems  (Fig.  12).  The  position  of 
these  nodes  is  indicated  by  the  so-called  "  eyes,"  which  are 
young  buds  in  the  axils  of  more  or  less  evident  scales  (which 
in  this  case  might  be  called  "  eyebrows  ")  .  The  cultivation  of 
potatoes  will  be  described  later,  but  in  this  connection  the 
preparation  and  planting  of  the  cuttings  will  be  indicated. 
The  tuber  is  cut  in  such  a  way  that  each  piece  to  be  used  for 
planting  contains  one  or  two  eyes;  and  at  the  same  time 
each  piece  must  contain  as  much  food  material  as  possible. 
The  bud  (eye)  is  a  young  shoot,  capable  of  developing  a  stem 
with  its  leaves,  and  the  node  in  the  proper  soil  conditions  can 
also  put  out  roots.  This  means  the  organization  of  a  new 


OTHER   METHODS   OF   PROPAGATION 


329 


plant,  but  until  it  is  established  and  independent,  it  must 
depend  upon  the  food  stored  up  in  the  old  tuber.  It  is  evi- 
dent, therefore,  that  the  node,  with  its  bud,  must  be  in  con- 
nection with  as  much  of  the  old  tuber  as  possible,  if  the  new 
plants  are  to  start  rapidly  and  vigorously.  The  depth  of 
planting  is  different  for  early  and  late  potatoes,  being  two  or 
three  inches  in  the  former  case,  and  nearly  twice  as  deep  in 
the  latter.  The  character 
of  the  soil  and  the  nature 
of  the  cultivation  for  this 
very  important  crop  will 
be  considered  in  another 
connection. 

The  same  general  prin- 
ciples, applied  with  differ- 
ent details,  appear  in  prop- 
agating by  root-cuttings, 
as  in  the  case  of  raspber- 
ries, sweet  potatoes,  etc., 
or  by  leaf -cuttings,  as  in 
the  case  of  begonias. 

31  a.  Layering. — Propa- 
gation by  layering  is  really 
only  a  modification  of 
propagation  by  cuttings, 
the  difference  being  that 

nodes  Of  the  Stem  are  made    FIG.  13.  —  Layering  a  plant,  as  a  rose  or  rasp- 

to  strike  root  before  they 

are  separated  from  the  parent  plant.  In  case  plants  can  be 
propagated  readily  by  cuttings,  the  less  convenient  method  of 
layering  is  not  used.  An  outline  of  the  method  is  as  fol- 
lows :  In  such  plants  as  certain  of  the  roses  and  raspberries, 
a  long  and  flexible  young  branch  is  bent  down  to  the  ground, 
fastened  in  place,  and  the  end  carried  up  and  held  in  an 
upright  position  above  ground  (Fig.  13).  The  bent  portion 


330  ELEMENTARY    STUDIES   IN   BOTANY 

is  covered  with  good  soil,  which  puts  some  nodes  in  a  favor- 
able condition  for  striking  root.  It  facilitates  the  growth  of 
roots  if  the  bark  breaks  at  the  bend ;  in  some  cases  it  helps 
to  make  an  incision  near  the  node ;  and  sometimes  a  ring  of 
bark  is  removed.  In  this  way  an  independent  plant  may  be 
developed,  which  in  the  course  of  a  season  or  two  is  in  a 
condition  to  be  transplanted  into  a  permanent  bed. 

32.  Grafting.  —  The  process  of  grafting  is  the  insertion  of  a 
part  of  one  plant  into  another  so  that  the  inserted  part  grows 
supported  by  the  other  plant.  The  inserted  part  is  called 
the  scion,  and  the  plant  upon  which  it  is  grafted  is  called  the 
stock.  The  purpose  of  grafting  is  to  propagate  the  scion, 
which  represents  the  desired  plant.  There  are  several  condi- 
tions that  make  grafting  a  desirable  and  even  a  necessary 
process.  For  example,  in  the  case  of  fruit  trees,  to  propagate 
a  desired  variety  by  seed  is  a  long  and  uncertain  process. 
Even  if  the  time  were  short  between  seed-planting  and  fruit- 
bearing,  often  the  seedlings  do  not  come  true  and  the  fruit 
is  not  that  which  is  desired.  In  the  case  of  seedless  fruits, 
grafting  becomes  necessary  for  propagation.  Advantage  is 
taken  of  grafting  also  to  secure  varieties  of  fruits  in  regions 
that  are  unfavorable  to  scion-plants.  For  example,  peach 
trees  thrive  better  in  sandy  soils  of  the  southern  states  than 
do  plum  trees;  therefore  by  using  peach  tree  stocks  and 
grafting  into  them  plum  tree  scions,  the  plum  varieties  can 
be  secured  which  otherwise  would  be  impossible. 

It  is  evident  that  the  use  of  grafting  is  based  upon  the  fact 
that  the  scion  retains  its  individuality,  so  far  as  the  character 
of  its  fruit  is  concerned.  Much  has  been  written  concerning 
the  influence  of  stock  on  scion,  and  of  scion  on  stock,  but  in 
ordinary  practice  this  influence  is  negligible.  It  is  of  scien- 
tific interest  to  discover  how  unlike  plants  may  be  and  still 
enter  into  this  union,  but  the  fact  of  practical  importance  is 
that  the  more  closely  the  two  plants  are  related,  the  more 
successful  is  the  grafting. 


OTHER  METHODS   OF   PROPAGATION 


331 


Grafting  is  a  very  old  operation,  and  it  has  developed  into 
very  many  kinds.  In  this  connection  it  would  be  unprofit- 
able to  describe  many  methods,  for  such  detailed  knowledge  is 
necessary  only  for  those  who  are  making  a  special  study  of 
grafting.  A  few  common  methods  will  be  described,  and  they 
will  serve  to  illustrate  the  principles  involved. 

Cleft-grafting  is  a  method  very  commonly  used  with  fruit 
trees  (apple,  pear,  plum,  cherry,  etc.),  when  it  is  desired  to 
use  well-established  stock  plants  to  support  varieties  with 
more  desirable  fruit.  The  stock  plant  is  cut  off  at  a  suitable 
place,  the  stump  end  is  split  a  short 
distance  and  wedged,  the  wedge- 
shaped  base  of  the  scion  is  in- 
serted so  that  cambiums  of  scion 
and  stock  are  in  contact,  the 
wedges  are  removed,  and  the  whole 
surface  of  the  graft  is  covered  with 
grafting  wax,  which  protects  the 
wound  until  it  has  healed  and 
stock  and  scion  have  grown  to- 
gether. To  double  the  chances  of 
success  it  is  very  common  to  insert 
two  scions  into  a  single  cleft,  for 
the  cambium  is  near  the  surface,  FIG  u  —  cieft-grafting  •  in  the 
and  a  scion  on  each  side  of  the  cleft  %*£"$£  £UT  £  '^Tii 

Will  be  in  proper  position  (Fig.  14).          covered    with    grafting    wax. — 
_.  .  After  BAILEY. 

The  scions  usually  include  three 

nodes  (buds),  and  are  cut  from  twigs  of  the  previous  season. 
These  twigs  are  stored  for  a  time  in  a  cool  place  and  pass 
into  a  dormant  condition.  It  is  customary  to  insert  the 
scion  so  that  one  of  the  buds  is  at  the  surface  of  the  graft, 
and  this  bud,  although  covered  by  the  grafting  wax,  has  the 
best  chance  to  grow. 

The  use  of  a  twig  as  a  scion  is  what  is  ordinarily  meant  by 
grafting,  and  in  addition  to  cleft-grafting,  described  above, 


332 


ELEMENTARY   STUDIES   IN   BOTANY 


FIG.   15.  —  Whip-grafting.  —  After  BAILEY. 


there  is  whip-grafting,  in  which  scion  and  stock  of  equal  size 
are  spliced  and  lashed  together  (Fig.  15) ;  inarching,  in  which 
two  potted  plants,  for  example,  are  brought  together,  and 

the  scion  is  fastened 
to  the  stock  without 
separation  from  the 
parent  plant  until 
union  has  been  secured ;  bridge- grafting,  in  which  the  stock  is 
girdled,  and  dormant  scions,  wedge-shaped  at  each  end,  are 
inserted  at  each  edge  of  the  girdle  and  bound  in  (Fig.  16). 

33.  Budding.  —  In  addition  to  the  use  of  twigs  as  scions, 
which  may  be  called  true  grafting,  it  is  very  common  to  use 
buds  as  scions,  a  method  which  is  bud-grafting,  but  is  usually 
called  simply  budding.  This  consists  in  in- 
serting under  the  bark  of  a  stock  plant  a  bud 
that  has  been  removed  from  a  scion  plant. 
It  is  performed  in  spring  or  autumn,  when 
the  bark  peels  easily,  and  is  frequently  used, 
instead  of  twig-grafting,  in  the  propagation 
of  desirable  races  of  fruits,  especially  of  the 
stone  fruits.  The  bud  is  sliced  from  its  stem 
so  as  to  include  a  little  of  the  wood  beneath  ; 
the  leaves  are  removed  from  the  stock  in  the 
region  to  be  grafted ;  cross  slits  (usually  like 
a  T)  are  made  through  the  bark  of  the  stock ; 
the  base  of  the  bud  is  slipped  beneath  the 
flaps  of  bark  and  bound  in  position ;  and  in 
two  or  three  weeks  the  bud  "  sets  "  and  the 
wrapping  is  removed. 

All  of  the  operations  described  in  this 
chapter  are  merely  illustrations  of  a  very  extensive  practice 
of  vegetative  propagation.  As  opportunity  offers,  such  opera- 
tions should  be  witnessed  in  orchards,  nurseries,  greenhouses, 
etc.  Furthermore,  if  suitable  plants  are  available,  some  of 
the  simpler  operations  should  be  undertaken  by  the  students. 


FIG.  16.  —  Bridge- 
grafting.  —  After 
BAILEY. 


CHAPTER  VI 
PLANT-BREEDING 

34.  Definition.  —  By  "  plant-breeding  "  is  meant  the  im- 
provement of  our  old  plants  and  the  securing  of  new  ones. 
Great  advances  have  been  made  recently  in  our  knowledge 
in  reference  to  plant-breeding.     These  advances  have  largely 
been  due  to  the  fact  that  scientific  men  have  been  experiment- 
ing with  plants  to  discover  what  are  called  the  laws  of  hered- 
ity, and  how  new  kinds  of  plants  are  produced.     All  this 
work  of  scientific  plant-breeders  has  suggested  to  practical 
plant-breeders  how  their  methods  may  be  improved.     Since 
a  better  and  a  more  abundant  food  supply  depends  upon  the 
progress  of  plant-breeding,  it  is  evident  that  it  is  a  subject 
of  the  greatest  importance. 

35.  Seed  firms.  —  The  work  of  practical  plant-breeding  is 
done  chiefly  by  establishments  that  have  made  it  a  specialty, 
and  that  provide  improved  races  of  plants  and  new  plants 
for  the  use  of  those  who  cultivate  them.     For  example,  the 
farmer   seldom   works   at   plant-breeding,    but   secures  his 
seed  from  "  seed  firms  "  that  are  equipped  to  do  the  more 
careful  work  that  plant-breeding  requires. 

36.  Department  of  Agriculture.  —  In  addition  to  the  work 
of  the  seed  firms,  the  United  States  government,  through 
its  Department  of  Agriculture,  does  a  vast  amount  of  work 
in  both  scientific  and  practical  plant-breeding,  the  results 
of  which  are  for  the  benefit  of  all  those  who  wish  to  cultivate 
plants.     This    Department    also    publishes    a    great    many 
bulletins  dealing  with  all  kinds  of  operations  connected  with 
the  cultivation  of  all  kinds  of  plants,  and  these  bulletins  may 
usually  be  obtained  for  the  asking.     It  would  be  a  wise  thing 

333 


334  ELEMENTARY   STUDIES   IN   BOTANY 

for  each  school  to  secure  a  set  of  these  bulletins  dealing  with 
the  prominent  crops  of  the  vicinity. 

37.  State  Experiment  Stations.  —  The  same  sort  of  work 
and  the  same  free  distribution  of  information  is  going  on  at 
the  various  State  Agricultural  Experiment  Stations,  and  the 
bulletins  from  the  station  in  its  own  state  should  certainly 
be  obtained  by  each  school. 

Although  the  national  government  and  the  state  govern- 
ments and  the  seed  firms  are  all  at  work  on  the  problems 
of  plant-breeding,  so  that  the  cultivator  of  plants  may  take 
their  results  and  use  them,  yet  the  intelligent  cultivator 
should  know  something  of  the  methods  and  possibilities  of 
plant-breeding.  This  knowledge  will  at  least  give  him  a 
more  critical  j  udgment  in  reference  to  the  claims  made  by  the 
practical  plant-breeders. 

38.  Mass  culture.  —  The  oldest  method  of  plant-breeding 
is  called  mass  culture,  a  method  which  has  done  much  in 
securing  improved  races  of  plants.     It  may  be  explained  by 
using  wheat  as  an   illustration.     The   plant-breeder   selects 
some  feature  of  the  wheat  he  wishes  to  improve  ;  for  example, 
its  yield.     He  goes  through  a  wheat  field  and  selects  the  indi- 
vidual plants  whose  heads  bear  the  largest  number  of  grains. 
The  grains  from  these  selected  plants  are  saved  for  seed,  and 
in  the  next  season  they  are  planted  and  produce  a  crop. 
The  plant-breeder  goes  through  the  new  field  and  again  selects 
the  best  individuals,  and  their  grain  is  saved  for  seed.     This 
selection  goes  on  year  after  year,  and  each  succeeding  year 
shows  a  somewhat  larger  yield  than  the  year  before.     Pres- 
ently by  this  method  of  "  continuous  selection  "  the  larger 
yield  reaches  a  standard  and  a  steadiness  that  enables  the 
plant-breeder  to  announce  an  improved  race  of  wheat,  that  is, 
a  race  improved  as  to  its  yield. 

This  method  of  plant-breeding  has  certain  disadvantages 
that  are  obvious.  It  requires  a  great  deal  of  time  and  labor, 
and  when  the  improved  race  is  put  into  the  hands  of  an 


PLANT-BREEDING  335 

ordinary  farmer  it  does  not  stay  improved  very  long.  Unless 
the  farmer  uses  great  care  in  his  own  selection  of  individuals 
for  seed,  he  will  mix  poor  individuals  with  good  ones  and  his 
succeeding  crops  will  degenerate.  For  this  reason,  such 
farmers  must  apply  frequently  to  the  plant-breeders  for  a 
new  supply  of  "  guarded  stock,"  that  is,  seeds  from  individ- 
uals that  have  been  carefully  selected  and  kept  separate  from 
the  undesirable  ones. 

39.  Pedigree  culture.  —  Another  method  of  plant-breeding 
that  has  come  into  prominence  more  recently  is  called  pedigree 
culture,  which  means  that  a  single  plant  is  selected  and  its 
progeny  carefully  guarded,  rather  than  hundreds  of  plants. 
It  is  the  method  ordinarily  used  in  breeding  fine  animals. 
For  a  long  time  animals  have  not  been  improved  by  the  pas- 
ture-full, but  by  the  individual,  whose  pedigree  is  carefully 
recorded.     It  is  a  well-known  fact  that  no  two  individuals 
are  exactly  alike,  so  that  in  even  the  most  careful  mass 
culture  many  kinds  of  individuals  are  mixed,  and  the  result 
is  an  average.     In  pedigree  culture  it  is  not  an  average  of 
many  good  individuals  that  is  secured,  but  the  very  best 
individual. 

The  advantages  of  pedigree  culture  over  mass  culture  are 
obvious.  The  selected  individual  is  farther  along  in  the  right 
direction  to  start  with,  and  so  time  and  labor  are  saved; 
and  also  it  is  found  that  the  result  is  more  constant  and  less 
likely  to  degenerate.  However,  the  best  results  are  obtained 
by  combining  the  two  methods ;  for  even  after  pedigree  cul- 
ture has  selected  out  a  desirable  race,  it  may  be  improved  by 
mass  culture. 

40.  Disease-resistance.  —  In    connection    with    pedigree 
culture  it  has  become  possible  to  combat  disease  and  drought 
with  remarkable  success.     These  are  the  two  most  serious 
enemies  to  cultivated  plants,  and  our  annual  losses  from  these 
two  causes  are  very  large.     A  few  notable  cases  will  serve  to 
illustrate  the  method. 


336  ELEMENTARY    STUDIES   IN   BOTANY 

A  few  years  ago  the  cotton  fields  of  the  southern  states 
were  attacked  by  a  very  destructive  disease.  When  the 
ravaged  fields  were  examined  by  experts,  it  was  discovered 
that  certain  cotton  plants  were  untouched  by  the  disease ; 
in  other  words,  these  individuals  were  immune  to  this  partic- 
ular disease.  This  fact  suggested  that  this  immunity  might 
be  a  character  that  could  be  inherited,  and  so  immune  indi- 
viduals were  selected  for  breeding,  and  it  was  found  that  their 
progeny  was  also  immune.  In  this  way,  by  pedigree  culture, 
immune  races  of  cotton  have  been  developed.  It  must  not 
be  supposed  that  an  immune  race  is  immune  under  all  condi- 
tions, but  this  method  enormously  increases  our  success  in 
preventing  disease.  This  same  method  can  be  applied  to  all 
plants  for  all  diseases,  so  that  it  is  possible  to  look  forward  to 
the  time  when  we  will  be  cultivating  only  disease-resistant 
races  of  plants. 

41.  Drought-resistance.  —  A  few  years  ago  the  wild  orig- 
inal of  our  cultivated  wheat  was  discovered  in  Palestine. 
This  wild  wheat  grows  in  dry  conditions,  in  situations  that  we 
would  call  "  arid/'  such  as  are  found  in  this  country  in  New 
Mexico  and  Arizona.  A  drought-resistant  wheat  would  be 
of  the  first  importance,  provided  it  was  also  of  good  quality. 
This  combination  of  drought-resistance  and  good  quality 
has  now  been  secured  through  plant-breeding,  so  that  it  has 
become  possible  to  insure  wheat  crops  against  drought. 
More  than  that,  the  drought-resistant  wheat  thus  secured 
is  found  to  be  disease-resistant ;  that  is,  to  the  rust  disease. 
This  combination  of  drought-resistance,  disease-resistance, 
and  good  quality  promises  to  increase  greatly  the  production 
of  wheat. 

A  peculiar  race  of  corn  has  been  found  in  cultivation  in 
China,  which  has  a  structure  that  makes  it  drought-resistant. 
Corn  is  peculiarly  in  danger  of  drought  during  the  period 
when  pollination  occurs,  and  if  a  "  dry  spell  "  occurs  at  that 
period  the  corn  crop  is  seriously  damaged.  If  this  drought- 


PLANT-BREEDING  337 

resistant  character  can  be  combined  with  good  quality  of 
grain  and  good  yield,  the  result  will  be  of  very  great  impor- 
tance. This  work  is  under  progress,  but  the  results  have  not 
been  announced. 

These  illustrations  from  wheat  and  corn,  our  two  most  im- 
portant cereal  crops,  indicate  the  possibility  of  breeding 
drought-resistant  races  of  all  the  important  cultivated  plants. 

42.  Corn-breeding.  —  It  would  not  be  fair  to  give  the 
impression  that  plant-breeding  is  a  simple  problem  and  that 
all  plants  can  be  handled  alike.  The  breeding  of  corn  will 
serve  to  illustrate  how  difficult  the  problem  often  is.  A  great 
deal  of  corn-breeding  has  been  done,  and  it  is  still  one  of  our 
most  important  problems,  for  corn  is  not  only  one  of  our  most 
important  cereals,  but  it  is  probably  the  most  difficult  one 
for  the  plant-breeder  to  handle.  The  ordinary  field  of  corn 
is  a  remarkable  mixture  of  different  kinds  of  individuals,  so 
that  ordinary  mass  culture  reaches  very  indefinite  results. 
The  discovery  that  the  best  method  of  selection  is  to  select 
the  best  ears  rather  than  merely  the  most  vigorous  individuals 
has  resulted  in  a  very  largely  increased  yield.  One  difficulty 
in  connection  with  corn,  however,  is  that  pollination  is  so 
free  that  under  ordinary  conditions  it  is  beyond  control. 
During  the  four  or  five  days  when  a  young  ear  is  being  pol- 
linated, the  pollen  is  flying  freely  from  the  tassels  of  many 
plants,  so  that  some  of  the  kernels  of  an  ear  may  have  received 
undesirable  pollen.  Therefore,  after  a  good  ear  has  been 
selected  for  seed,  it  may  contain  undesirable  hybrid  kernels. 
This  means  that  selection  must  be  continuous,  not  only  to 
secure  desirable  individuals,  but  also  to  weed  out  undesirable 
hybrids.  It  is  obvious  that  in  this  case  pedigree  culture 
deals  with  pedigrees  known  on  the  female  (ear)  side  and  only 
vaguely  known  on  the  male  (tassel)  side. 

When  rigid  pedigree  culture  is  applied  to  corn,  so  that  pol- 
lination is  accomplished  under  control,  and  a  pure  strain  is 
secured,  free  from  all  mixture  with  other  kinds  of  individuals, 


338  ELEMENTARY   STUDIES   IN   BOTANY 

it  has  been  found  that  this  pure  strain  deteriorates  to  a  cer- 
tain level ;  in  other  words,  it  is  not  so  good  for  our  purposes 
as  the  mixed  races.  In  this  case  it  is  found  that  if  two  pure 
strains  are  crossed,  the  resulting  hybrids  are  more  vigorous 
than  either  parent.  The  ideal  corn-breeding,  therefore,  is 
rather  a  complex  operation,  involving  two  distinct  operations  : 
(1)  pedigree  culture,  which  separates  pure  strains  from  a 
mixture;  (2)  combination  of  pure  strains,  which  secures 
vigorous  plants.  The  question  might  be  asked,  why  is  it 
desirable  to  separate  pure  strains  from  mixtures,  only  to 
combine  them  again  in  new  mixtures?  The  answer  is  that 
unless  the  pure  strains  are  separated  and  recombined,  the 
mixtures  are  chance  mixtures  rather  than  intelligent  mixtures. 
There  are  very  many  people,  however,  who  prefer  to  use 
chance  rather  than  intelligence. 

43.  Hybridization.  —  In  the  operations  of  plant-breeding 
described  above,  reference  was  made  to  "  crossing  "  ;  that  is, 
the  use  of  two  parent  plants  of  different  kinds,  resulting  in 
what  is  called  a  hybrid.  Hybridization  is  a  very  important 
operation  in  plant-breeding,  for  by  means  of  it  certain  desir- 
able qualities  that  are  separated  in  two  kinds  of  plants  may  be 
combined  in  a  single  individual.  It  must  not  be  supposed 
that  the  desired  combination  will  appear  in  all  of  the  hybrid 
progeny.  It  is  only  when  thousands  of  hybrids  are  produced 
that  there  is  any  certainty  that  the  desired  combination  will 
be  found  among  them.  But  when  it  is  found,  the  plant 
possessing  it  can  be  pedigreed  and  multiplied. 

There  is  a  limitation  in  the  use  of  hybrids  that  must  be 
noted.  A  hybrid  combines  characters  of  two  parents,  and 
when  it  produces  progeny  by  means  of  seeds,  only  about  one- 
half  of  the  new  individuals  will  continue  the  combination, 
that  is,  will  continue  to  be  hybrids.  The  other  half  will 
resemble  one  or  the  other  parent.  This  is  what  is  called 
the  "  splitting  "  of  hybrids,  and  they  split  up  in  a  definite 
ratio,  which  is  called  Mendel's  law,  and  this  same  ratio  of 


PLANT-BREEDING  339 

splitting  appears  in  each  succeeding  generation.  In  propa- 
gating a  hybrid  by  seed,  therefore,  one  may  expect  that  in 
ordinary  conditions  only  about  one-half  the  progeny  will 
show  the  desired  combination. 

It  follows,  therefore,  that  hybridization  is  most  useful  with 
those  plants  that  are  not  propagated  by  seed,  but  by  some 
vegetative  method,  as  by  tubers,  bulbs,  cuttings,  layering, 
grafting,  etc. ;  for  in  these  cases  one  hybrid  individual  is 
continued  directly  in  its  progeny,  without  bringing  in  another 
plant  as  a  parent.  It  is  evident  that  the  method  can  be  used 
with  great  efficiency  among  the  fruits,  which  are  so  largely 
propagated  vegetatively ;  but  that  it  is  by  no  means  so 
efficient  among  the  cereals,  which  must  be  propagated  by 
seeds. 

A  few  illustrations  will  fix  the  method  in  mind.  Seedless 
apples  of  poor  quality  have  long  been  known,  but  by  crossing 
seedless  apples  with  those  of  good  quality,  a  hybrid  was  pro- 
duced which  combined  the  two  desired  characters.  It  is 
evident  that  in  this  case  vegetative  propagation  is  necessary, 
so  that  there  would  be  no  danger  of  the  hybrid  splitting  in  the 
ordinary  way. 

The  ordinary  cultivated  blackberry  is  large  and  black, 
but  there  is  a  small  wild  blackberry  that  is  whitish  or  cream 
color.  By  crossing  the  two,  a  hybrid  was  secured  that  pro- 
duced berries  of  the  large  size  and  light  color,  so  that  "  white 
blackberries  "  could  be  grown. 

The  possibilities  of  such  combinations  are  endless  and  many 
of  them  have  been  made,  some  more  curious  than  useful, 
but  many  of  them  very  useful. 

Enough  has  been  said  to  show  that  the  operations  of  plant- 
breeding  are  exceedingly  varied,  and  that  by  the  use  of  various 
methods,  either  singly  or  in  combination,  almost  any  desired 
result  may  be  obtained.  It  is  becoming  almost  literally  true 
that  one  may  order  almost  any  kind  of  plant  and  expect  to 
have  the  order  filled. 


340  ELEMENTARY   STUDIES   IN   BOTANY 

44.  Selection    for    regions.  —  One    important    fact    con- 
nected with  plant-breeding  needs  to  be  emphasized.     The 
natural  tendency  is  for  cultivators  of  plants  to  attempt  to 
grow  the  same  kinds  of  plants  everywhere.     If  natural  vege- 
tation is  observed,  it  will  be  observed  that  the  assemblages 
of  plants,  technically  known  as  the   "  plant  population," 
differ  in  different  regions,  which  means  that  nature  does  not 
attempt  to  grow  the  same  plants  everywhere.     It  is  obvious 
that  for  every  region  there  is  the  most  suitable  group  of  culti- 
vated plants,  that  is,  plants  that  will  do  the  best.     If  this  is 
considered,  each  region  can  be  made  to  yield  its  maximum 
of  plant  products,  which  would  greatly  increase  the  total 
production  of  a  large  country  like  the  United  States. 

45.  The  food  problem.  —  The  food  problem  is  one  of  the 
most  important  problems  of  this  country.     It  has  become  a 
problem  because  the  rate  of  increase  of  population  is  much 
larger  than  the  rate  of  increase  of  food  production.     It  is 
evident  that  this  inequality  of  the  two  rates  must  not  be 
allowed  to  continue  indefinitely.     The  recent  developments 
in  plant-breeding,   indicated  in  the  preceding  paragraphs, 
together  with  the  increase  of  knowledge  in  reference  to  the 
nature  of  the  soil  and  its  manipulation,  outlined  in  Chapter 
III,  make  it  possible  to  multiply  many  times  the  plant  prod- 
ucts of  the  country.     This  becomes  evident  if  the  following 
possibilities  are  realized : 

1 .  Securing  plants  of  largest  yield  and  most  desirable  qual- 
ity through  the  various  methods  of  plant-breeding. 

2.  Securing  disease-resistant  races,   by  means   of  which 
frequent  and  great  loss  in  plant  products  can  be  prevented. 

3.  Securing  drought-resistant  races,  by  means  of  which 
crops  can  not  only  be  insured  against  drought  where  they  are 
grown  now,  but  their  cultivation  can  be  extended  into  new 
regions,  especially  those  which  have  been  regarded  as  too  dry 
for  such  plants. 

4.  Selection  for  each  region  of  the  group  of  cultivated 


PLANT-BREEDING  341 

plants  best  fitted  for  the  conditions,  by  means  of  which  the 
maximum  yield  of  plant  products  can  be  secured  for  each 
region. 

5.  Cultivation  of  the  soil  in  such  a  way  that  it  may  be  kept 
in  the  best  physical  condition  from  the  time  of  planting  to  the 
time  of  harvesting. 

Experience  has  shown  that  when  any  one  of  these  five 
possibilities  is  realized,  the  amount  of  plant  product  is  much 
increased ;  and  it  becomes  evident  that  when  all  five  of  them 
are  realized  throughout  the  country,  our  food  production  will 
be  multiplied  many  times. 

Another  important  factor  that  enters  into  the  explanation 
of  our  diminishing  food  supply  in  comparison  with  our  popu- 
lation is  the  persistent  movement  of  population  from  the 
country  to  the  cities,  changing  producers  of  food  into  mere 
consumers  of  food.  Now  that  agriculture  is  becoming  as 
scientific  a  profession  as  engineering  or  medicine,  it  is  to  be 
hoped  that  it  will  be  attractive  to  an  increasing  number  of 
vigorous  young  men,  who  might  well  recoil  from  the  blind 
drudgery  of  the  old-time  farm,  but  will  welcome  the  new  and 
highly  important  science  of  agriculture. 


23 


CHAPTER   VII 

CEREALS  AND  FORAGE  PLANTS 
CEREALS 

46.  General  statement.  —  The  cereals  must  be  regarded 
as  the  most  important  crop  plants  of  the  world.  They  are 
grasses  that  have  been  brought  into  cultivation  on  account 
of  the  abundant  starch  stored  in  their  seeds.  This  starch 
is  not  only  the  basis  of  our."  bread-stuffs/'  but  it  also  feeds 
the  animals  from  which  we  obtain  our  principal  meat  supply, 
as  well  as  those  we  use  in  other  ways.  The  cultivation  of  cere- 
als is  the  chief  business  of  agriculture,  so  far  as  plants  are 
concerned,  and  among  the  cereals  are  plants  that  have  been 
cultivated  throughout  the  whole  recorded  history  of  man. 
In  fact,  it  was  probably  the  cultivation  of  cereals,  more  than 
any  other  cause,  that  first  transformed  wandering  tribes  of 
men  into  settled,  agricultural  people. 

The  important  cereals  are  corn,  oats,  wheat,  barley,  and 
rye,  and  the  order  given  represents  their  relative  importance 
in  the  United  States  at  the  present  time. 

In  considering  the  cultivation  of  cereals  in  the  United 
States,  the  student  should  know  not  only  the  methods  of  cul- 
tivation, but  also  the  range  of  cultivation  and  the  relative 
importance  of  each  crop.  The  statistics  given  have  been 
obtained  from  the  most  recent  information  in  possession  of 
the  United  States  Department  of  Agriculture.  They  are 
given  in  round  numbers,  but  they  will  reveal  the  relative 
importance  of  our  cereals  as  at  present  cultivated.  It  must 
also  be  remembered  that  the  amount  of  production  varies 
from  year  to  year,  dependent  upon  what  are  called  "  good 

342 


CEREALS   AND   FORAGE    PLANTS 


343 


years  "  and  "  bad  years  "  for  such  crops.  The  cereals  will 
be  considered  in  the  order  of  their  importance  in  the  United 
States. 

Corn  (Maize) 

47.  Production  of  corn.  —  A  more  appropriate  name  for 
Indian  corn  is  "  maize,"  the  original  name  given  to  it  when 
America  was  discovered.  In  foreign  countries,  "  corn " 
means  any  grain  and  several  things  besides.  "  Indian  corn  " 


FIG.  17.  —  Map  shaded  to  show  the  states  of  greatest  corn-production. 

distinguishes  it  from  any  other  grain,  but  the  simple  word 
"  corn  "  distinguishes  it  only  in  the  United  States. 

The  United  States  is  preeminently  the  country  of  corn-pro- 
duction, in  1912  producing  over  three  billion  bushels.  This 
statement  is  emphasized  by  contrasting  this  production  with 
that  of  other  countries,  which  will  have  to  be  done  for  the  year 
1911.  In  that  year,  a  relatively  poor  year,  the  United  States 
produced  two  and  a  half  billion  bushels  of  corn,  while  Italy, 
the  second  country  in  corn-production,  produced  93  million 
bushels,  and  Russia  81  million  bushels.  In  fact,  in  1910  (the 


344 


ELEMENTARY    STUDIES   IN   BOTANY 


last  year  for  which  returns  from  all  countries  are  available), 
the  United  States  produced  nearly  three-fourths  of  the  corn 

of  the  world,  a 
ratio  which  prob- 
ably still  holds. 

The  greatest 
corn-producing 
state  is  Illinois 
(about  335  mil- 
lion bushels  in 
1911),  and  the 
record  for  Iowa 
is  almost  as  large 
(about  305  mil- 
lion bushels  in 
1911).  No  other 
states  were  re- 
ported as  pro- 
ducing more 
than  200  million 
bushels  in  1911, 
the  order  of  the 
larger  records 
being  Missouri, 
Indiana,  Ne- 
braska, Ohio, 
and  Kansas.  In 
the  government 
statistics  re- 
ferred to,  18  states  are  included  as  corn-producing  states,  the 
remaining  11,  in  the  order  of  amount  of  production,  being 
Kentucky,  Tennessee,  Minnesota,  Texas,  Pennsylvania, 
Georgia,  Wisconsin,  Michigan,  Mississippi,  Alabama,  and 
South  Dakota.  This  enumeration  of  states  emphasizes  the 
fact  that  "the  com  lands  occur  in  the  central  and  southern 


FIG.  18.  —  Corn :  the  plant  at  the  right  shows  the  stami- 
nate  flowers  forming  the  terminal  "tassel"  ;  the  plant  to 
the  left  shows  the  "ear"  (a  close  cluster  of  pistillate 
flowers)  in  the  axil  of  a  leaf  and  enclosed  by  the  "husk," 
at  the  end  of  which  the  long  styles  ("silk")  are  exposed. 
—  After 


CEREALS  AND  FORAGE  PLANTS       345 

states,   or  practically  within  the   drainage   system   of  the 
Mississippi  River  (Fig.  17). 

48.  Structure   of  corn.  —  Any  one  who   cultivates   corn 
should  know  something  of  its  structure,  which  is  quite  dif- 
ferent from  that  of  the  other  cereals  (Fig.  18).     There  are  two 
kinds  of  flowers,  one  containing  the  stamens  and  the  other 
the  pistil.     The  staminate  flowers  form  a  spreading  cluster 
at  the  top  of  the  plant,  constituting  what  is  commonly  called 
the  "  tassel."     An  examination  of  this  tassel  shows  that  it 
is  made  up  of  numerous  small  flowers,  each  one  of  which  con- 
sists of  bracts  enclosing  three  stamens  whose  anthers  are  soon 
seen  hanging  downward,  suspended  by  the  long  and  slender 
filaments. 

The  flowers  with  the  pistils  are  in  a  close  cluster  upon  a 
branch  from  the  axil  of  a  leaf.  It  is  this  branch  that  forms 
the  "  cob,"  and  upon  it  the  pistillate  flowers  stand  close 
together  in  longitudinal  rows.  The  branch  is  ensheathed  by 
large  bracts,  which  later  form  the  "  husk  "  that  invests  the 
ear.  Each  flower  consists  of  small  bracts  enclosing  a  single 
pistil,  whose  long,  thread-like  style  forms  the  so-called  "  silk." 
It  is  the  silk  that  receives  the  pollen  from  the  stamens,  and 
through  the  silk  the  pollen  tube  carries  the  male  cell  to  the 
egg.  In  this  way  fertilization  occurs,  and  as  a  consequence 
the  grains  begin  to  develop  and  later  the  mature  "  ear  "  is 
formed. 

The  danger  from  drought  occurs  when  the  pollen  is  flying, 
for  at  that  time  the  silk  must  be  moist  to  receive  the  pollen 
and  to  start  the  growth  of  the  pollen-tube.  Since  four  or 
five  days  are  consumed  in  fully  pollinating  a  single  ear,  which 
means  that  each  silk  must  catch  and  hold  some  pollen,  it  is 
evident  that  a  drying  wind,  or  even  dry  air,  will  endanger  the 
process.  This  is  the  most  critical  period  for  the  corn  crop, 
for  blasted  silk  means  failure  of  fertilization. 

49.  Cultivation  of  corn.  —  In  the  cultivation  of  corn,  only 
general  principles  can  be  mentioned  here.     There  are  many 


346  ELEMENTARY    STUDIES   IN   BOTANY 

details  that  develop  and  should  be  learned  in  connection  with 
the  practice.  The  cultivation  of  no  cereal  has  received  so 
much  attention  in  recent  years,  and,  as  a  result,  it  is  neces- 
sary for  the  corn-grower  to  keep  informed  as  to  the  results  of 
experimental  work.  Even  the  preparatory  ploughing  varies 
as  to  time  and  depth  and  other  details. 

While  corn  is  grown  on  a  great  variety  of  soils,  the  best  corn 
is  produced  upon  deep,  rich,  well-watered  and  well-drained 
soils.  A  rich  soil  usually  means  one  with  a  large  amount  of 
organic  material  in  such  condition  that  it  is  loose  and  friable, 
and  not  likely  to  cake  in  dry  weather.  A  soil  with  such 
physical  properties  is  often  described  as  a  "  sandy  loam." 
It  has  great  capacity  for -receiving  water  and  retaining  it  as 
soil  films,  and  at  the  same  time  drains  so  readily  that  the 
circulation  of  the  air  is  not  interfered  with.  The  depth  and 
perfect  physical  condition  of  the  soil  demanded  by  successful 
corn-production  is  greater  than  for  any  other  cereal  crop. 
In  preparing  such  a  soil  for  seed,  it  is  usually  ploughed  deeper 
than  for  any  other  cereal  crop,  but  it  is  not  certain  that  this 
is  necessary. 

In  the  greatest  corn-producing  states,  the  deeper,  pre- 
liminary ploughing  is  generally  done  in  the  fall,  and  during  the 
following  May  the  seed-bed  is  finally  prepared  and  planted. 
The  time  of  planting  is  planned  so  as  to  escape  the  late  spring 
frosts.  The  sowing  is  done  either  in  hills  or  drills,  but  in 
any  event  it  is  done  so  that  the  soil  can  be  worked  between 
the  rows  of  corn.  The  ground  is  kept  pulverized  with  the 
harrow  until  the  young  plants  appear ;  and  afterwards  the 
same  pulverizing  is  accomplished  by  running  cultivators 
of  various  kinds  between  the  rows.  This  is  continued  as 
long  as  it  can  be  done  without  injury  to  the  plants,  usually 
extending  for  about  six  weeks  from  the  first  of  June. 

50.  Selection  of  corn.  —  Very  much  attention  has  been 
paid  to  the  selection  of  seed  corn,  and  to  arouse  interest  and 
to  develop  facility  in  selection,  as  well  as  to  stimulate  interest 


CEREALS   AND   FORAGE   PLANTS 


347 


in  agriculture  in  general,  there  has  been  an  extensive  organ- 
ization of  "  corn  clubs  "  for  boys  in  rural  communities. 
Reference  has  been  made  to  these  clubs  (p.  320),  but  in  this 
connection  the  principles  of  selection  will  be  outlined  briefly. 
The  two  chief  factors  in  the  selection  are  a  suitable  plant  and 

a  suitable  ear.    The  plant  should  ^ 

be  vigorous,  with  all  its  members 
(roots,  stem,  and  leaves)  well 
developed.  The  selected  ear 
should  be  early  maturing,  large, 
sound,  well  shaped  (carrying  its 
diameter  well  from  butt  to  tip), 
with  straight  and  compact  rows 
of  grains,  and  a  cob  about  one- 
half  the  diameter  of  the  ear  (Fig. 
19).  The  selected  ears  should 
be  stored  in  a  dry  place,  with 
uniform  temperature ;  and  be- 
fore planting  the  grains  should 
be  tested  for  vitality  in  a  germi- 
nating bed,  usually  called  a 
"  tester."  The  direction  for 
club  work  is  that  no  lot  of  grains 
should  be  used  for  planting  that 

do    not    Show   by   the    testing    Of    FIG.  19.  —  Two  ears  of  corn,  showing  a 

samples  that  at  least  95  per  cent 
of  them  germinate  promptly  and 
vigorously. 

51.  Corn-tester.  —  There  are  several  kinds  of  testers,  but 
one  that  can  be  constructed  in  any  school  or  home  is  the 
"sawdust  box,"  which  is  exceedingly  satisfactory  (Fig.  20). 
A  box  three  or  four  inches  deep  and  about  thirty  inches 
square  is  recommended  as  a  good  size.  This  is  half  filled  with 
thoroughly  moistened  sawdust  (soaked  for  at  least  an  hour), 
pressed  down  and  with  a  smooth  surface.  Upon  the  sawdust 


348 


ELEMENTARY    STUDIES   IN   BOTANY 


FIG.  20.  —  The  "sawdust  box"  for  testing 
corn  :  explained  in  text.  —  After  Iowa 
State  College  Bulletin. 


surface  is  laid  a  strong  white  cloth  ruled  in  numbered  squares 
with  sides  two  or  three  inches  long.     This  cloth  is  held  in 

place  by  being  tacked  to  the 
box.  As  many  ears  of  corn 
can  be  tested  as  there  are 
squares  on  the  cloth,  and 
each  ear  must  bear  a  number 
corresponding  to  a  numbered 
square.  From  each  ear  six 
kernels  are  removed :  one 
from  near  the  base  of  the  ear, 
one  from  the  middle,  and  one 
from  near  the  tip,  and  three 
others  in  the  corresponding 
positions  on  the  opposite  side  of  the  ear.  These  six  kernels, 
selected  as  samples  of  the  entire  ear,  are  placed  upon  the 
square  of  cloth  whose  number  corresponds  to  that  of  the  ear. 
When  all  the  kernels  to  be  tested  have  been  placed  in 
their  proper  positions  on  the  cloth,  another  cloth  is  laid  over 
them  and  sprinkled.  Then  another 
cloth,  larger  than  the  box,  is  placed 
upon  the  sprinkled  cloth,  shaped  as  a 
lining  to  the  box,  and  covered  with  two 
inches  of  moist  and  pressed-down  saw- 
dust, over  which  the  edges  of  the  large 
cloth  are  folded  (Fig.  20).  If  kept  in 
a  warm  place,  the  grains  will  germinate 
in  about  six  days,  when  the  cover  is 
removed  carefully  so  as  not  to  displace 
them.  The  condition  for  examination 
is  when  shoots  (stems)  are  about  two 
inches  long,  and  if  it  is  discovered  that 
the  grains  have  been  uncovered  too 
soon,  the  covering  should  be  replaced.  Each  ear  is  repre- 
sented by  six  kernels,  and  if  one  or  more  of  the  kernels  have 


FIG.  21.  —  Section  of  a  grain 
of  corn :  explained  in  the 
text.  —  After  FRANK. 


CEREALS   AND   FORAGE   PLANTS 


349 


failed  to  germinate,  or  some  of  the  seedlings  are  decidedly 
weaker  than  the  others,  that  ear  should  be  discarded. 

The  germination  of  corn  is  illustrated  in  Figs.  21-27.  In 
Fig.  21  is  shown  a  section  of  a  grain  of  corn.  Within  the 
testa,  the  contents  are  divided  into  two  principal  regions,  that 
to  the  right  and  below  being  the  embryo, 
and  that  to  the  left  and  above,  the  endo- 
sperm, in  which  the  food  is  stored.  The 
position  of  the  embryo  is  peculiar,  for  in- 
stead of  being  surrounded  by  the  endo- 
sperm, it  lies  to  one  side  of  it.  It  will  be 
noticed  that  the  single  large  cotyledon  of 
the  embryo  is  in  contact  with  the  endo- 
sperm, from  which  it  obtains  food  which  it 
passes  on  to  the  growing  parts  that  are  to 
escape  from  the  seed.  In  the  embryo  may 
also  be  seen  the  bud  that  is  to  produce 
the  stem  and  leaves,  and  below  it  the 
hypocotyl  that  is  to  escape  first  and  estab- 
lish the  root  system.  The  cotyledon  is 
attached  at  the  joint  which  separates  the 
young  stem  and  the  hypocotyl.  The  figure 
also  indicates  that  the  endosperm  has  two 
regions :  the  outer  region  (more  deeply 
shaded)  is  the  "  horny  endosperm,"  which 
contains  protein  food  in  addition  to  its 
starch ;  while  the  inner  region  (with  lighter 
shading)  is  the  " starchy  endosperm."  As  the  relative  size  of 
the  two  regions  varies,  the  richness  of  the  grain  in  protein 
or  in  starch  varies.  Figures  22  and  23  are  slightly  different 
views  of  a  sprouting  grain,  showing  the  superficial  position  of 
the  embryo,  and  that  it  simply  splits  a  membrane  (the  testa) 
to  be  completely  exposed.  Figures  24-26  are  all  in  the  same 
position,  Fig.  24  showing  the  tip  of  the  hypocotyl  turning 
towards  the  ground ;  Fig.  25  showing  the  great  elongation  of 


FIGS.  22  and  23.  — Two 
views  of  sprouting 
grains  of  corn,  show- 
ing the  relation  of 
the  embryo  to  the 
food  supply ;  the 
"sprout"  is  the  tip 
of  the  hypocotyl. 


350 


ELEMENTARY   STUDIES   IN   BOTANY 


the  hypocotyl,  the  beginning  of  growth  and  curving  upward 
of  the  stem,  and  the  putting  out  of  roots  ;  while  in  Fig.  26 
the  growth  of  all  the  parts  has  pro- 
ceeded still  further.  In  Fig.  27  is  shown 
a  young  seedling  established  for  inde- 
pendent work,  with  the  root  system 
started  and  the  leaves  beginning  to 
unfold. 

The  value  of  testing  for  vitality  be- 
fore planting  is  indicated  by  the  follow- 
ing statement  from  a  recent  bulletin 
(February,  1913)  issued  by  the  State 
Agricultural  Experiment  Station  of 
Iowa: 

"  Testing  the  vitality  of  seed  corn  be- 
fore planting  in- 
creased the  profits 
per   acre   93.6  per 
cent   in    1910   and 

gg  7  c    nt      m 

191  1  ,  or  an  increase 

of  19.6  bushels  per  acre  in  1910  and  of 
10.1    bushels  in  1911." 

52.  Sweet  corn  —  In  addition  to  field 
corn  of  various  kinds,  there  are  the 
numerous  races  of  sweet  corn.  Sweet 
corn  is  to  be  regarded  as  a  vegetable 
rather  than  a  cereal,  but  the  soil  condi- 
tions and  the  principles  of  cultivation  are 
the  same  as  for  field  corn.  It  is  more 
intensively  cultivated  than  field  corn, 
and  to  this  end  it  is  planted  in  hills  rather 
than  drills,  so  that  the  soil  all  about  it 
may  be  kept  in  condition.  Canned  sweet  corn  has  become 
so  common  a  food  in  North  America  that  the  demand  for  it 


FIGS.    24-26.  —  stages  in 

the  germination  of  corn: 
explained  m  the  text. 


FIG.  27.  —  A  young  corn 
seedling  just  after  ger- 
mination has  been 
completed. 


CEREALS  AND  FORAGE  PLANTS       351 

has  developed  extensive  cultivation  of  sweet  corn  for  this  pur- 
pose, the  leading  states  in  the  amount  of  this  product  being 
New  York,  Maine,  Illinois,  and  Iowa,  in  the  order  named. 

Oats 

53.  Production  of  oats.  —  The  United  States  is  also  the 
leading  country  in  the  production  of  oats,  in  1912  producing 
nearly  one  and  a  half  billion  bushels.  The  contrast  with  other 


FIG.  28.  —  Map  shaded  to  show  the  states  of  greatest  oat-production. 

countries  may  be  illustrated  by  the  crops  of  1911,  when  the 
United  States  produced  922  million  bushels,  and  Russia  pro- 
duced 858  million  bushels.  These  two  great  oat-producing 
countries  were  followed  by  Germany  with  530  million 
bushels. 

Within  the  United  States,  Iowa  and  Illinois  produce  the 
largest  amount,  in  1911  Iowa  producing  126  million  bushels 
and  Illinois  121  million  bushels.  This  represents  a  little 
over  one-quarter  of  the  amount  produced  by  all  the  states. 
The  other  states  reported  as  oat-producing  states,  in  the  order 
of  the  amount  of  production,  are  Minnesota,  Wisconsin,  Ohio, 


352 


ELEMENTARY   STUDIES   IN   BOTANY 


and  North  Dakota.  This  means  that 
the  states  of  the  Upper  Mississippi  Valley 
region  produce  most  of  our  oats  (Fig. 
28). 

54.  Structure  of  oats.  —  The  structure 
of  oats  is  more  like  that  of  the  ordinary 
grasses  than  is  the  structure  of  corn.  The 
flowers  are  in  a  loose,  branching  cluster 
(panicle),  each  little  group  of  flowers 
(spikelet)  with  a  stalk  of  its  own  (Figs.  29 
and  30).  Each  spikelet  consists  of  two 
relatively  large  bracts  (glumes)  that  sur- 
round usually  two  flowers  (Fig.  30,  B). 
Each  flower  consists  of  a  pistil  (whose 
ovary  becomes  the  grain)  and  three  sta- 
mens infolded  by  a  bract  (palet) ,  and  usu- 
ally the  palet  of  one  of  the  flowers  bears 
on  its  back  (Fig.  30,  C)  a  long,  bristle-like 
appendage  (awn).  It  is  these  awns  that 
in  many  grasses,  as  the  other  cereals,  form 
the  so-called  "  beard."  The  prominent 
feature  that  distinguishes  oats  from 
wheat,  barley,  and  rye  is  the  loose, 
branching  cluster  of  stalked  spikelets.  In 
these  other  cereals  the  spikelets  stand  close 
together  on  the  main  axis,  forming  the 
cluster  called  a  spike,  which  is  the  so-called 
"  head  "  of  wheat,  etc. 
FIG.  29. —  Oats,  showing  55.  Cultivation  of  oats,  —  The  oat  is  a 

general  habit  of  plant ;     ,  ,     .  „    .  i      v 

flower  cluster  distin-  hardy  cereal,  doing  well  in  a  cool  climate 
ShtabnychSgg  S  and  upon  a  light  soil,  and  therefore  it  is 
each  spikelet  on  a  sien-  o-rown  chiefly  in  northern  countries.  In 

der  stalk.  J 

fact,  it  is  not  at  all  suited  to  the  ordinary 
tropical  conditions.  The  range  of  conditions  in  which  it  will 
grow  is  somewhat  extensive,  including  light  soils  and  heavy 


CEREALS   AND    FORAGE    PLANTS 


353 


soils,  cool  climate  and  warm  climate,  but  it  is  not  able  to 
endure  an  excess  of  water. 

In  connection  with  the  sowing  of  oats,  the  soil  is  not  always 
ploughed  when  it  is  rich  and  deep,  as  corn  land,  but  the  seeds 
are  sown  broadcast  and  then  covered  by  means  of  a  corn- 
cultivator  or  a  spe- 
cial harrow,  being 
smoothed  over  after- 
wards by  an  ordinary 
harrow.  Upon  gen- 
eral principles,  how- 
ever, a  good  seed-bed 
should  be  prepared  by 
ploughing,  not  neces- 
sarily so  deep  as  for 
other  cereals,  and  pul- 
verizing. Most  of  the 
oats  are  sown  early 
in  the  spring,  so  that 
most  of  the  growth, 
which  takes  approxi- 
mately three  months,  FlG  30._Oats>  showing  detaila  of  flower  clus~ter:  AI 
may  occur  during  the 
cooler  part  of  the 
growing  season.  Oat3 
are  also  sown  in  the 
fall  ("  winter  oats  "), 
but  this  practice  seems  to  be  restricted  to  the  more  southern 
areas  of  oat-cultivation. 


part  of  the  cluster,  showing  the  stalked  spikelets ; 
B,  a  single  spikelet,  showing  the  two  glumes  enclos- 
ing two  flowers  (a  third  abortive  one  is  shown), 
each  consisting  of  a  pistil  (whose  branching  style  is 
shown)  and  three  stamens  infolded  by  the  palet ;  C, 
the  palets  of  the  two  flowers,  one  of  them  with  a  long 
awn.  —  After  SARGENT. 


Wheat 

56.  Production  of  wheat.  —  It  is  perhaps  a  surprise  to  some 
that  the  United  States  produces  less  wheat  than  oats,  the 
amount  for  1912  being  730  million  bushels.  Nevertheless, 


354 


ELEMENTARY    STUDIES   IN   BOTANY 


it  produces  more  wheat  than  any  other  country,  Russia 
being  second,  and  India  third.  In  1911  the  product  from 
these  three  countries  was  621  million  bushels  in  the  United 
States,  509  million  bushels  in  Russia,  and  369  million  bushels 
in  India. 

Within  the  United  States,  North  Dakota  produces  the 
most  wheat  (about  73  million  bushels  in  1911),  and  the  other 
wheat-producing  states  come  in  the  following  order  :  Kansas, 


FIG.  31.  —  Map  shaded  to  show  the  states  of  greatest  wheat-production. 

Washington,  Minnesota,  Illinois,  Nebraska,  Ohio,  Missouri, 
Indiana,  Michigan,  and  Pennsylvania.  It  will  be  noticed 
that  these  are  all  north  central  states  excepting  Washington 
(Fig.  31). 

57.  Structure  of  wheat.  —  It  is  easy  to  distinguish  wheat 
(Fig.  32),  with  its  spikes  (heads),  from  oats,  with  its  panicles 
(spreading  clusters) ;  but  barley  and  rye  also  have  spikes,  and 
one  should  be  able  to  distinguish  wheat  at  sight  from  these 
cereals.  Wheat  and  rye  are  alike  in  having  a  single  spikelet 
at  each  joint  of  the  axis ;  while  in  barley  each  joint  bears 
three  spikelets  (one  or  two  of  which  may  be  poorly  developed). 


CEREALS  AND   FORAGE   PLANTS 


355 


The  most  obvious  distinction  between  wheat  and  rye  is  that 
in  wheat  each  spikelet  contains  several  perfect  flowers,  while 
in  rye  each  spikelet  contains  two  perfect  flowers.  There  are 
many  races  of  wheat,  but  the  conspicuous  difference  in  the 
heads  is  that  some  are  "  bearded  "  (with 
awns)  and  some  are  "  beardless  "  (without 
awns)  (Fig.  33). 

58.  Discovery  of  wild  wheat. — The  cul- 
tivation of  wheat  is  the  oldest  recorded 
agricultural  operation,  and  wheat  is  per- 
haps still  to  be  regarded  as  the  most  valu- 
able of  cereals.  The  wild  original  of  the 
wheat  was  long  sought  for,  and  it  was  sup- 
posed that  it  had  been  so  long  in  cultiva- 
tion that  it  must  have  become  very  much 
changed  and  probably  was  represented  in 
nature  by  some  inconspicuous  grass.  It 
seemed  clear  that  if  wild  wheat  still  existed, 
it  would  be  found  in  western  Asia.  A  few 
years  ago  a  Jewish  botanist  found  the  wild 
original  of  wheat  growing  upon  the  rocky 
slopes  of  the  mountains  of  Palestine,  and 
it  did  not  look  very  different  from  culti- 
vated wheat.  It  is  clear  now  that  our  an- 
cestors who  began  the  cultivation  of  wheat 
did  not  select  an  inconspicuous  grass,  fore- 
seeing that  it  might  be  changed  into  a  very  useful  plant,  but 
took  a  grass  that  was  plainly  useful  already.  In  fact,  this 
wild  wheat  is  a  better  plant  for  our  purpose  in  several  par- 
ticulars than  our  cultivated  races.  It  grows  in  thin  and  dry 
soils,  quite  unlike  the  soil  necessary  for  the  cultivated  races 
of  wheat,  which  have  become  pampered  by  being  transferred 
to  better  soils.  Not  only  is  this  wild  wheat  drought-resistant, 
but  its  vigor  is  further  shown  by  the  fact  that  it  is  not  sus- 
ceptible to  the  attack  of  the  rust  disease,  one  of  the  most 


FlG.  32. — Wheat,  show- 
ing general  habit  of 
plant ;  the  flower 
cluster  is  a  spike. 


356 


ELEMENTARY   STUDIES   IN   BOTANY 


destructive  diseases  of  our  pampered  and  weakened  races  of 
wheat.  It  is  obvious  that  this  discovery  of  wild  wheat,  with 
its  drought-resistant  and  disease-resistant  qualities,  is  full  of 
possibilities  in  the  development  of  races  of  wheat  suitable  for 
the  drier  regions  of  our  country,  thus  enormously  extending 
the  area  of  wheat-cultivation.  In  certain  parts  of  these  arid 
regions,  what  is  called  "  dry  farming  "  has  been  developed, 
which  means  the  retention  of  moisture  in  the  soil  by  proper 
tillage;  and  in  these  regions  a  race  of 
wheat  called  "  Durum "  has  been  used 
with  marked  success.  This  Durum  wheat 
is  a  race  that  is  more  closely  related  to 
wild  wheat  than  any  other  cultivated  race, 
and  for  this  reason  it  is  more  drought- 
resistant  than  the  ordinary  races. 

59.  Cultivation  of  wheat.  —  Wheat  has 
been  cultivated  for  so  long  a  time  and 
under  so  many  conditions  that  it  has 
more  varieties  or  races  than  any  other 
cereal,  and  to  select  the  best  race  of  wheat 
for  a  given  area  demands  the  judgment 
of  an  expert.  There  are  spring  and  win- 
ter wheats,  bearded  and  beardless  wheats, 
soft  and  hard  wheats,  etc.,  and  new  races 
of  all  of  these  are  being  announced  almost  every  year.  . 

The  cultivated  wheats  require  good  soil,  better  than  oats 
will  thrive  in,  and  a  thoroughly  pulverized  soil,  so  as  to  secure 
a  high  degree  of  water-holding  capacity,  and  at  the  same 
time  good  drainage. 

In  preparing  the  soil  for  winter  wheat,  it  is  ploughed  four  or 
five  inches  deep,  then  pulverized,  and  allowed  to  settle  before 
the  seed  is  sown.  The  seed  is  often  sown  broadcast  and  then 
covered  with  a  harrow,  but  more  commonly  now  it  is  drilled, 
a  method  which  secures  more  even  distribution  and  more 
uniform  depth.  Wheat  is  a  hardy  plant  in  enduring  cold, 


FIG.  33.— "Bearded"  and 
"beardless"  wheat.  — 
After  Internat.  Encyl. 


CEREALS  AND  FORAGE  PLANTS       357 

but  the  best  protection  of  young  winter  wheat  is  a  covering  of 
snow,  under  which  it  can  endure  freezing  temperatures.  The 
greatest  danger  to  winter  wheat  is  the  alternate  thawing  and 
freezing  of  an  unprotected  soil. 

Spring  wheat  is  sown  as  early  as  possible,  to  secure  the 
cooler  part  of  the  growing  season  for  the  principal  growth,  and 
usually  upon  soil  that  has  been  ploughed  the  previous  autumn, 
or  often  without  ploughing  upon  a  corn-field  of  the  preceding 


FIG.  34.  —  Map  shaded  to  show  the  states  of  greatest  barley-production. 

season.  In  the  case  of  ploughing  and  preparing  a  seed-bed,  the 
seed  is  broadcast  or  drilled  as  described  above.  In  the  case 
of  planting  among  corn-stubble,  it  is  broadcast  and  covered 
by  a  corn-cultivator  and  frequent  harrowing. 

Barley 

60.  Production  of  barley.  —  The  great  barley-producing 
country  of  the  world  is  Russia,  which  reported  411  million 
bushels  in  1911 ;  while  the  United  States  came  second 
with  only  160  million  bushels.  In  1912  the  United  States, 
produced  224  million  bushels. 
24 


358 


ELEMENTARY    STUDIES   IN   BOTANY 


Within  this  country,  California  produces  the  most  barley 
(about  40  million  bushels  in  1911),  and  the  other  barley-pro- 
ducing states  come  in  the  following  order  :  Minnesota,  North 
Dakota,  Wisconsin,  Iowa,  Washington, 
Idaho,  and  South  Dakota.  It  is  evident 
that  the  production  of  barley  is  not  re- 
stricted by  suitable  conditions,  but  by  lack 
of  general  interest  (Fig.  34). 

61.  Cultivation  of  barley.  —  Barley  is 
also  a  cereal  of  very  ancient  cultivation, 
and  has  been  found  in  its  original  wild 
state  in  western  Asia  (Fig.  35)  .  Its  range 
of  cultivation  is  very  great,  extending  far- 
ther north  than  the  usual  range  of  wheat, 
and  extending  southward  into  tropical 
conditions.  It  also  grows  quickly,  and 
therefore  can  be  used  in  regions  of  short 
growing  seasons. 

The  soil  conditions  and  preparation  are 
approximately  the  same  as  for  wheat. 
Most  of  our  barley,  at  least  in  the  northern 
states,  is  sown  in  the  spring.  Barley  is  a 
little  more  sensitive  to  cold  than  wheat,  so 
that  in  regions  where  wheat,  oats,  and  bar- 
ley are  grown,  the  order  of  planting  is  first 
spring  wheat,  then  barley,  and  finally  oats. 
The  methods  of  sowing  (broadcast  and 
drill)  are  the  same  as  for  wheat. 
FlGin3g5g7nerlrieh^t°^f  The  cultivation  of  winter  barley  is  in- 
piant  and  character  creasing  rapidly,  because  it  gives  a  better 

of  spike.  .  .  .     . 

yield  than  spring  barley,  and  is  a  more 
certain  crop.  At  present  its  cultivation  is  chiefly  in  the 
states  south  of  the  Ohio  and  Platte  rivers  and  those  west  of 
the  Rocky  Mountains.  The  Department  of  Agriculture  has 
indicated  those  states  in  which  only  spring  barley  can  be 


CEREALS  AND  FORAGE  PLANTS       359 

grown,  those  in  which  only  winter  barley  can  be  grown,  and 
those  in  which  both  can  be  grown. 

Rye 

62.  Production  of  rye.  —  The  United  States  makes  its 
poorest  showing,  so  far  as  cereals  are  concerned,  in  the  culti- 
vation of  rye,  coming  fifth  in  the  list  of  rye-producing  coun- 
tries. Russia  is  far  in  advance  of  any  other  country,  with 


FIG.  36.  —  Map  shaded  to  show  the  states  of  greatest  rye-production. 

762  million  bushels  in  1911,  followed  by  Germany  with  427 
million  bushels,  then  Austria-Hungary,  France,  and  the 
United  States  (33  million  bushels).  In  1912  the  United 
States  produced  35  million  bushels,  the  most  productive 
state  being  Wisconsin,  followed  by  Michigan,  Minnesota, 
Pennsylvania,  New  York,  New  Jersey,  and  Indiana  (Fig.  36). 
63.  Cultivation  of  rye.  —  Rye  seems  to  have  been  intro- 
duced into  cultivation  later  than  the  other  cereals,  for  the 
records  of  it  do  not  extend  beyond  the  Roman  agriculture. 
For  this  reason,  probably,  there  are  fewer  kinds  of  rye  than 


360 


ELEMENTARY   STUDIES   IN   BOTANY 


of  any  other  cereal  (Fig.  37) .  Its  great  feature  in  cultivation 
is  that  it  will  grow  in  soil  too  poor  for  any  other  cereal.  It 
cannot  grow  so  far  north  as  barley,  but  it  can  ripen  in  lati- 
tudes too  cold  for  wheat.  However,  it  thrives  best  where 
wheat  thrives,  but  as  it  is  not  so  valuable  a 
crop,  it  does  not  replace  wheat. 

It  is  usually  cultivated  on  light,  sandy 
soils,  not  doing  at  all  well  on  wet  and 
heavy  soils.  As  in  the  case  of  the  other 
cereals,  there  are  spring  and  winter  ryes, 
the  latter  being  most  frequently  used,  and 
usually  ripening  in  June.  The  preparation 
of  the  soil,  the  planting,  and  the  cultivation 
are  the  same  as  for  the  other  cereals. 

Rice 

64.  Production  of  rice.  —  If  the  impor- 
tant cereal  crops  of  the  whole  world  were 
being  considered,  rice  would  have  to  be 
added,  for  it  is  estimated  to  supply  the 
principal  food  of  one-half  the  human  race. 
But  very  little  of  the  rice  of  the  world  is 
produced  in  the  United  States  (715  million 
pounds  in  1911),  and  its  production  is  re- 
stricted practically  to  the  Gulf  states  and 
Arkansas,  with  Louisiana  producing  by  far 
the  largest  amount  (Fig.  38) .  The  greatest 
rice-producing  country  in  the  world  is  India  (about  89  billion 
pounds  in  1910),  and  Japan  is  the  next  in  our  records  (about  15 
billion  pounds  in  1910).  The  statistics  of  rice-production  in 
China  are  not  available,  but  it  must  be  much  greater  than  that 
of  Japan ;  and  Egypt  is  also  a  great  rice-producing  country. 
65.  Structure  of  rice.  —  The  appearance  of  the  flower 
cluster  of  rice  is  intermediate  between  that  of  barley  and  oats 
(Fig.  39).  The  spikelets  are  in  a  panicle,  as  in  oats,  but  the 


FIG.  37.  —  Rye,  show- 
ing general  habit  of 
plant  (upper  part  of 
stem  omitted)  and 
character  of  spike. 


CEREALS  AND  FORAGE  PLANTS       361 

branches  of  the  panicle  are  erect  and  often  crowded,  not 
spreading,  as  in  oats,  but  not  compact  and  looking  like  a 
spike,  as  in  barley.  There  is  a  single  perfect  flower  in  each 
spikelet,  and  the  hard  palet  encloses  the  grain  so  closely  that 
it  falls  with  it,  forming  the  so-called  "husk"  about  the  grain 
(Figs.  40  and  41).  Rice  with  the  husks  on  is  often  called 
"  paddy,"  while  in  India  all  rice  is  "  paddy." 


FIG.  38.  —  Map  shaded  to  show  the  states  of.greatest  rice-production. 

66.  Cultivation  of  rice.  —  The  cultivation  of  rice  belongs 
to  subtropical  countries,  and  it  requires  wet  soil,  which  can 
be  artificially  flooded  at  certain  times.  There  are  also 
"  upland  "  varieties  which  do  not  require  flooding.  In  the 
warmer  countries  two  crops  a  year  are  raised.  The  seed  is 
sown  on  very  wet  soil,  then  transplanted  to  its  permanent 
place,  and  flooded  at  intervals.  In  the  United  States  the 
rice  lands  are  prepared  as  for  other  cereals,  and  either  put 
under  irrigation  control,  or  lowlands  are  used  that  are  subject 
to  flooding.  Of  course  the  upland  rice  is  cultivated  in  the 
dry  way  used  with  other  cereals. 


362 


ELEMENTARY   STUDIES   IN   BOTANY 


FOKAGE  PLANTS 

67.  Definition.  —  Forage  plants  are  those  used  as  food  for 
farm  animals,  and  their  cultivation  forms  a  very  important 
part  of  agriculture.  Foods  for  animals  have  been  developed 
recently  in  such  variety  that  they  have  extended  far  beyond 

the  range  of  forage  plants,  but 
the  latter  are  the  only  animal 
foods  that  come  within  the  pur- 
pose of  this  book.  Forage  plants 
also  include  those  that  are  not 
cultivated  primarily  as  animal 
foods,  as,  for  example,  the  use  of 
corn  fodder,  straw,  and  cereal 
grains  as  such  foods.  These  have 
been  considered  under  the  head 
of  cereals. 

68.  The  grass  family.  —  The 
most  ancient  forage  plants  are 
the  grasses,,  and  every  one  is  fa- 
miliar with  their  use  for  grazing 
and  for  hay.  Until  recently,  hay 
always  meant  dried  grass,  but 
other  kinds  of  hay  (dried  plants) 
have  been  added.  Naturally  the 
grasses  are  still  the  most  used 
forage  plants,  for  pastures  (for 
grazing)  and  meadows  (for  cut- 
ting) occur  extensively  in  nature 
and  involve  the  least  amount  of  cultivation.  Conspicuous 
among  the  grasses  that  have  been  Cultivated  for  pasture  and 
meadow  purposes  are  redtop,  timothy,  and  Kentucky  blue 
grass,  and  samples  of  these  three  grasses  should  be  examined, 
so  that  they  can  be  recognized. 

69.  The  legume  family.  —  In  addition  to  the  grasses,  there 


FIG.  39-41.  — Rice:  Fig.  39,  the 
flower  cluster;  fig.  40,  a  single 
flower,  with  its  bracts;  fig.  41, 
bracts  removed,  showing  the  grain 
infolded  by  the  husk.  —  The  single 
flowers  after  BAILLON. 


CEREALS   AND   FORAGE   PLANTS  363 

are  three  great  forage  plants,  which  are  used  also  for  other 
purposes.  They  are  clover,  alfalfa,  and  cow-pea,  and  any 
outline  of  agricultural  operations  which  does  not  include  these 
great  crops  would  be  incomplete.  They  all  belong  to  a  single 
great  family  (Leguminosse) ,  and  associated  with  them  are 
such  familiar  plants  as  sweet  peas,  common  peas,  beans, 
peanuts,  and  such  trees  as  the  locusts  and  redbuds. 

These  three  forage  plants  have  a  very  important  character 
in  common,  which  can  be  described  for  all  of  them.  They  are 
all  able  to  use  the  free  nitrogen  of  the  air  by  their  peculiar 
association  with  the  nitrogen-fixing  bacteria  of  the  soil. 
This  means  that  instead  of  drawing  upon  the  very  important 
nitrates  of  the  soil,  they  can  add  to  the  nitrates  and  thus 
enrich  the  soil.  For  this  reason  they  can  be  used  to  restore 
soil  that  has  become  impoverished  in  its  nitrogen  supply  by 
other  crops.  It  is  customary,  therefore,  to  alternate  crops  of 
these  clover-like  plants  with  other  crops,  notably  the  cereals, 
the  process  being  called  "  rotation  of  crops."  In  other 
words,  these  forage  plants  are  very  commonly  used  as  the 
"  alternating  crop  "  which  restores  the  soil  to  good  condition. 

These  plants  are  not  only  useful  in  adding  nitrogen  com- 
pounds to  the  soil,  but  they  are  also  remarkably  deep  rooted 
and  leave  the  soil  in  better  physical  condition.  The  deep- 
rooting  not  only  puts  the  soil  in  better  physical  condition, 
but  it  facilitates  the  movement  of  salts  towards  the  surface, 
so  that  the  result  of  such  a  crop  is  not  only  an  accumulation 
in  the  superficial  soil  of  nitrogen  compounds,  but  also  of  other 
important  soil  salts. 

Another  very  common  use  to  which  these  plants  are  put,  a 
use  which  depends  upon  their  rich  contents  of  valuable  salts, 
is  what  is  called  "  green  manuring,"  which  means  that  the 
plants  are  ploughed  into  the  soil  and  contribute  their  whole 
bodies  to  enriching  it. 

70.  Clover.  —  There  are  a  good  many  clovers,  but  the 
most  valuable  one  as  a  forage  plant  is  the  red  clover,  whose 


364 


ELEMENTARY   STUDIES   IN   BOTANY 


FIG.  42.  —  Red  clover. 


appearance,  with  its  three 
leaflets  (each  usually  with 
a  pale  spot  on  the  upper 
surface)  and  head  of  rose- 
purple  flowers,  should  be 
familiar  to  every  one 
(Fig.  42) .  It  is  extremely 
valuable  for  the  many 
purposes  it  serves,  such 
as  hay,  green  fodder,  pas- 
turage, green  manuring, 
but  its  chief  value  is  in 
enriching  the  soil,  as  de- 
scribed above.  It  is  used 
also  as  a  "  cover-crop" 
in  orchards,  which  means 

that  it  can  cover  the  soil  in  such  a  way  as  to  hold  the  moist- 
ure, at  the  same  time  enriching  the  soil.  Later  it  is  "  ploughed 
under/'  and  it  contributes  still  more 
to  the  soil. 

Red  clover  can  grow  in  a  variety 
of  soils  and  climates,  but  at  present 
its  most  extensive  agricultural  use  is 
in  the  northern  states. 

71.  Alfalfa.  —  This  forage  plant 
(called  also  lucerne),  a  native  of 
western  Asia,  and  long  cultivated  in 
Europe,  has  become  extensively  cul- 
tivated in  the  western  states  (Fig. 
43).  It  was  introduced  into  Cali- 
fornia about  sixty  years  ago,  and  its 
cultivation  has  extended  rapidly  over 
the  arid  regions  of  the  Pacific  and  FIQ  43.  _  Alfalfai  showing  the 

Rocky  Mountain   States,  where  it  is         ^  general  habit,  a  single  flower, 

,  ,  and  the  curiously  coiled  pod. 

grown   more    extensively  than   any        —After  in.  of  British  Flora. 


CEREALS  AND  FORAGE  PLANTS       365 

other  forage  crop.  Its  cultivation  is  extending  still  further 
east,  and  it  bids  fair  to  replace  red  clover  in  many  of  our 
northern  states. 

The  best  soil  for  alfalfa  is  a  rich,  sandy,  well-drained  loam, 
and  this  makes  it  especially  favorable  for  the  rich  soils  of  the 
dry  west  where  irrigation  is  used.  It  is  a  plant  one  to  three 
feet  high,  with  clover-like  leaves,  and  purple  flowers  in  long, 
loose  clusters.  In  loose  soils  the  tap-root  is  said  to  reach  a 


FIG.  44.  —  Cow-pea.  —  After  ENGLER  and  PRANTL. 

depth  of  ten  to  twelve  feet,  and  cases  of  50  feet  in  depth 
have  been  reported. 

The  seeds  are  sown  broadcast  or  in  drills,  and  the  young 
plants  are  rather  tender,  so  that  care  is  necessary  to  establish 
a  field,  which  usually  requires  two  years,  but  after  it  has  been 
established  it  is  quite  enduring.  The  ordinary  yield  of  hay 
is  reported  to  be  three  to  eight  tons  per  acre,  and  sometimes 
a  yield  of  ten  to  twelve  tons  per  acre  is  reached. 

72.  Cow-pea.  —  Cow-pea  is  to  the  south  what  clover  is  to 
the  north  and  alfalfa  to  the  west.  It  is  an  important  hay 


366  ELEMENTARY   STUDIES   IN   BOTANY 

crop  and  soil-renovator  in  the  south,  and  it  is  grown  to  some 
extent  in  the  north  (Fig.  44).  It  is  a  bean,  rather  than  a 
pea,  closely  related  to  the  ordinary  garden  bean,  and  the 
beans  are  often  used  for  food.  In  the  south  the  plant  grows 
as  a  vine,  but  it  becomes  bushy  in  the  north. 

73.  Suggestions  for  work.  —  It  is  evident  that  the  growth 
of  cereal  and  forage  crops  cannot  be  made  a  part  of  the  work 
of  the  student.  Much  of  this  chapter,  therefore,  must  be  used 
as  information  concerning  these  very  important  crops. 
However,  two  things  should  be  done,  which  will  form  an  intro- 
duction to  crop-raising.  The  first  thing  is  to  learn  to  recog- 
nize the  cereals  and  forage  plants  mentioned  in  this  chapter. 
It  is  easy  to  secure  samples  of  the  plants  and  to  learn  their 
distinguishing  features.  The  second  thing  is  to  germinate 
and  test  some  of  the  seeds,  so  that  this  very  important  pre- 
liminary performance  may  be  learned  through  experience. 
Information  about  a  process  can  never  take  the  place  of 
experience.  Information  merely  suggests  how  the  process 
may  be  undertaken,  but  experience  encounters  all  of  the 
details  that  are  necessary  to  secure  the  result. 


CHAPTER  VIII 
VEGETABLES 

74.  Definition.  —  There  is  no  exact  definition  of  the  word 
vegetable.     Its  application  is  a  matter  of  usage,  including  the 
greatest  variety  of  plant  structures.     Even  the  same  plant 
product  may  be  called  a  vegetable  or  not ;  for  example,  corn 
is  either  a  vegetable  or  a  cereal,  dependent  upon  the  manner  of 
using  it.     While  the  cereals  all  belong  to  one  great  family,  the 
grass  family,  and  all  the  principal  fruits  belong  to  two  or  three 
families,  vegetables  belong  to  a  great  number  of  families. 
In  the  following  pages  representatives  of  ten  families  will  be 
presented  as  being  included  among  vegetables,  and  these 
are  selected  only  as  samples. 

Most  of  the  vegetables  are  cultivated  in  all  countries,  but 
each  country  is  characterized  by  the  emphasis  it  places  upon 
certain  vegetables.  For  example,  sweet  corn,  sweet  potatoes, 
tomatoes,  and  watermelons  are  cultivated  more  extensively 
in  the  United  States  than  anywhere  else  in  the  world.  These 
four  "  vegetables  "  will  serve  to  illustrate  the  great  variety  of 
structures  covered  by  the  name  :  one  is  a  seed,  one  is  a  root, 
and  two  are  fruits.  If  to  these  we  add  cabbage  and  lettuce, 
which  are  leaves,  onions,  which  are  bulbs,  and  potatoes, 
which  are  tubers,  we  find  that  at  least  six  different  plant  struc- 
tures are  included  in  the  term  vegetable. 

75.  Suggestions  for  work.  —  In  connection  with  the  work 
of  this  chapter,  not  only  ought  some  of  the  quick-growing 
vegetables  to  be  cultivated,  but  as  good  a  collection  of  vege- 
tables ought  to  be  brought  together  as  the  neighborhood 
affords.     An  interesting  "  field  trip  "  consists  in  visiting  some 
large  market,  where  the  different  vegetables  can  be  recog- 

367 


368  ELEMENTARY    STUDIES   IN   BOTANY 

nized.  It  is  surprising  how  many  young  people  there  are 
who  can  recognize  vegetables  when  served  on  the  table,  but 
who  cannot  recognize  many  of  them  as  they  appear  in  the 
markets. 

In  the  following  account  of  some  of  the  more  common  vege- 
tables, suggestions  as  to  cultivating  them  are  often  included, 
not  because  pupils  can  do  such  things  in  connection  with  this 
study,  but  because  they  should  know  something  of  such 
details,  and  chiefly  with  the  hope  that  some  of  them  may  be 
interested  in  cultivating  home  gardens. 

76.  Gardening.  —  The  cultivation  of  vegetables  is  usually 
called  gardening,  as  distinct  from  farming.     A  few  genera- 
tions ago  almost  every  family  had  a  home  garden,  the  prod- 
ucts of  which  were  for  family  use.     In  general,  this   was 
amateur  gardening,  and  the  results  were  extremely  variable. 
There  was  no  opportunity  to  select  especially  favorable  soil 
and  climate,  for  the  garden  had  to  be  near  the  home.     The 
general  purpose  was  to  secure  good  quality,  a  continuous 
supply,  and  as  great  variety  as  possible. 

With  the  growth  of  large  cities  a  new  phase  of  gardening 
was  developed,  known  as  market-gardening  or  truck-garden- 
ing, the  products  being  for  sale  just  as  are  the  products  of  a 
factory.  This  kind  of  gardening  became  professional,  and 
the  product  became  very  uniform  in  standard.  In  establish- 
ing an  industry  of  this  kind,  it  was  possible  to  select  the  most 
favorable  soil  and  climate,  sometimes  within  easy  reach  of 
the  market,  sometimes  at  great  distances  from  it.  The 
general  purpose  of  a  market  garden  is  to  secure  uniformity, 
high  productiveness,  quick  growth,  and  comparatively  few 
crops. 

77.  Garden  soil.  —  There  is  a  general  uniformity  in  the 
character  of  good  garden  soil,  no  matter  what  vegetables  are 
to  be  cultivated.     The  soil  should  be  not  only  rich  in  the 
materials  for  plant  food,  but  also  light  and  loose,  which  means 
good  drainage.     Such  a  soil  is  called  a  "  quick  "  soil  because 


VEGETABLES  369 

it  enables  plants  to  start  early  and  to  develop  rapidly.  Of 
course  it  must  be  tilled  thoroughly  and  kept  so.  The  plants 
are  also  stimulated  to  rapid  and  vigorous  growth  by  the  free 
use  of  suitable  fertilizers,  the  best  one  being  stable  manure. 
Where  intensive  gardening  is  practised,  many  vegetables  are 
started  under  glass  and  transplanted  as  soon  as  the  weather 
permits  (as  cabbage,  early  celery,  sweet  potatoes,  tomatoes, 
early  lettuce),  thus  securing  a  much  earlier  crop. 

78.  Classification  of  vegetables.  —  It  would  be  impossible 
and  unprofitable  to  enumerate  the  very  numerous  vegetables 
in  use.     Some  of  the  most  common  ones  must  be  selected  as 
representatives.     Any  one  who  knows  how  to  cultivate  these 
representative  forms  can  extend  the  same  principles  to  the 
cultivation  of  any  vegetable. 

Instead  of  classifying  vegetables  by  the  plant  families  to 
which  they  belong,  it  will  be  more  useful  to  classify  them  by  the 
plant  structures  they  represent.  This  is  more  useful  because 
it  is  the  structures  that  determine  the  methods  of  cultivation 
and  not  the  families.  The  six  structures  referred  to  above 
will  be  used:  (1)  tubers,  represented  by  the  potato;  (2)  roots, 
represented  by  the  radish,  turnip,  parsnip,  carrot,  beet,  and 
sweet  potato ;  (3)  bulbs,  represented  by  the  onion ;  (4)  leaves, 
represented  by  cabbage,  lettuce,  and  celery;  (5)  fruits, 
represented  by  the  tomato,  cucumber,  pumpkin,  squash,  and 
melons;  (6)  seeds,  represented  by  peas,  beans,  and  sweet 
corn.  Of  course  this  list  probably  does  not  include  all  of 
the  vegetables  cultivated  in  any  locality,  but  it  includes  the 
principal  ones. 

Tubers 

79.  Potato.  —  This   is   the   most   widely   cultivated   and 
valuable  of  the  tubers  used  as  vegetables.     The  potato  tuber 
is  a  thickened  branch  of  an  underground  stem  (Fig.  45),  and 
it  shows  its  stem  character  by  its  "  eyes,"  which  are  buds  in 
the  axils  of  minute  leaves  (scales).     America  is  the  native 


370 


ELEMENTARY    STUDIES   IN   BOTANY 


home  of  the  potato,  the  wild  plants  occurring  in  the  moun- 
tains and  highlands  from  southern  Colorado,  through  Mexico, 
and  south  into  Chili. 

Although  potatoes  originated  in  America,  they  are  not  so 
extensively  used  in  the  United  States  as  in  Europe.  For 
example,  in  the  ten  years  extending  from  1880  to  1890,  the 
average  annual  crop  of  the  United  States  was  170  million 

bushels,  while  that  of 
Europe  was  over  two 
billion  bushels.  In  1912, 
however,  the  crop  of  the 
United  States  had  be- 
come 421  million  bushels. 
In  1911  the  greatest 
potato-producing  states 
were  Wisconsin  (32  mil- 
lion bushels),  Michigan 
(31  million  bushels),  New 
York  (28  million  bushels), 
Minnesota  (26  million 
bushels),  and  Maine  (21 
million  bushels). 
The  potato  belongs  to  the  nightshade  family  (Solanacese), 
and  in  its  genus  (Solanum)  occur  not  only  the  poisonous 
nightshades,  but  also  the  edible  egg-plant ;  while  some  of  its 
associates  in  the  family  are  tomato,  red  pepper,  belladona, 
petunia,  and  tobacco.  The  flower  of  the  potato  plant  (Fig. 
46)  can  be  recognized  by  the  blue  or  white  corolla,  which  has 
five  broadly  spreading  lobes  ("  wheel-shaped  ") ;  and  its  five 
stamens  grouped  together  about  the  style,  with  anthers  open- 
ing by  a  hole  at  the  top.  The  fruit  produced  by  the  flower  is 
a  round  green  berry.  The  leaves  are  pinnately  compound, 
with  minute  leaflets  intermixed  with  the  large  ones. 

The  best  soil  for  potatoes  is  a  rich,  sandy,  well-drained 
loam,  forming  a  light  soil,  and  this  is  indicated  by  the  fact 


FIG.  45.  —  The  potato  plant,  showing  the  lower 
part  of  the  stem,  the  tubers,  and  the  roots.  — 
After  SARGENT. 


VEGETABLES 


371 


that  those  states  in  which  such  a  sandy  soil  occurs  in  abun- 
dance are  the  largest  producers.  Of  course  potatoes  are 
grown  in  cold,  damp  soil,  but  they  are  produced  more  quickly 
and  of  better  quality  in  rather  dry  and  sandy  soils. 

Cutting  the  tubers  for  planting  has  been  described  (p.  326). 
Each  piece  should  include  one  or  two  eyes  with  as  much  of 
the  tuber  attached  as  possible,  so  that  there  may  be  abundant 
food  to  start  the  young  plants  vigorously. 


FIG.  46.  —  The  potato  plant :    a,   foliage  and  flowers ;    b,   single  flower ;    c,   stamen, 
showing  the  terminal  pores  through  which  the  pollen  is  shed.  —  After  BAILLON. 

Early  potatoes  should  be  planted  as  soon  as  the  danger  of 
frost  is  past,  for  potatoes  are  sensitive  to  frost.  The  cuttings 
are  planted  two  or  three  inches  deep,  in  dry  and  warm  soil, 
and  in  tilling  the  ground  is  kept  level  until  the  plants  are 
nearly  full  grown.  Then  the  rows  are  "  hilled,"  which  makes 
the  soil  warmer  and  drier,  and  secures  an  earlier  develop- 
ment of  tubers. 

Late  potatoes  are  planted  three  or  four  weeks  after  the  early 
ones,  and  somewhat  deeper,  and  there  must  be  frequent  level 


372  ELEMENTARY   STUDIES   IN   BOTANY 

tillage  to  retain  the  soil  moisture  during  the  hot  weather  when 
the  tubers  are  maturing. 

There  are  hundreds  of  varieties  of  potatoes,  new  ones  con- 
stantly replacing  old  ones.  These  new  varieties  are  usually 
produced  under  exceptionally  favorable  conditions,  so  that 
in  ordinary  cultivation  they  degenerate  ("  run  out  ").  It 
is  for  this  reason  that  many  of  the  most  notable  varieties  of  a 
generation  ago  have  been  replaced  by  new  ones. 

Roots 

80.  Radish.  —  This  is  one  of  the  most  popular  vegetables, 
because  it  grows  quickly  and  is  ready  for  use  very  early  in  the 
season.  Since  it  can  be  grow^n  at  any  season  of  the  year  and 
develops  in  so  short  a  time,  it  is  one  of  the  best  garden  plants 
for  use  in  school  gardens,  as  well  as  in  home  gardens.  The 
radish  belongs  to  the  mustard  family  (Cruciferse) ,  which  con- 
tains many  common  wild  flowers  as  well  as  useful  plants. 
Associated  with  the  radish  in  the  same  family  are  such  useful 
plants  as  the  mustards,  water  cress,  horseradish,  cabbage, 
and  turnip.  The  family  is  recognized  by  its  four  petals 
(purple  and  whitish  in  radish),  its  six  stamens  (two  of  them 
shorter  than  the  other  four),  and  its  pod  fruit,  which  in  the 
radish  is  at  first  fleshy  and  then  becomes  dry  and  corky  (Fig. 
47). 

The  races  of  radish  differ  in  size,  shape,  color,  and  texture, 
as  any  one  who  sees  them  in  market  will  recognize  (Fig.  48). 
The  crop  is  much  more  uniform  if  the  seed  is  sifted  to  get  rid 
of  the  small  and  imperfect  seeds  and  of  foreign  particles  that 
are  apt  to  occur  in  any  package  of  seeds.  The  richer  and  looser 
the  soil,  the  better.  Spring  radishes  should  be  sown  as  soon 
as  the  ground  can  be  worked,  for  the  plants  are  very  hardy, 
and  radishes  will  be  ready  for  use  in  three  to  six  weeks.  In 
a  week  or  two  later  they  become  pithy,  so  that  repeated  sow- 
ings are  necessary  for  a  continuous  supply.  Summer  radishes 
are  of  slower  growth,  and  therefore  keep  longer  in  condition ; 


VEGETABLES 


373 


while  winter  radishes,  whose  seeds  are  sown  from  the  last  of 
July  to  the  middle  of  September,  are  still  slower  in  developing, 
and  may  be  kept  in  good  condition  almost  as  long  and  as  easily 
as  turnips.  The  planting  of  the  seeds  is  the  same  as  for  many 
garden  crops ;  that  is,  they  are  sown  in  rows  five  to  eight  inches- 


B 


FIG.  47.  —  A  flower  of  cabbage  (mustard  family)  :  A,  flower  cluster,  showing  buds- 
at  tip,  open  flowers  below  with  four  spreading  petals,  and  pods  at  the  bottom ; 
B,  a  mature  pod ;  C,  a  pod  opening.  —  After  WARMING. 

apart,  and  when  the  plants  appear,  so  that  relative  vigor  can 
be  recognized,  they  are  thinned  so  that  the  individual  plants 
stand  about  two  or  three  inches  apart  in  each  row. 

81.  Turnip.  —  The  turnip  (Fig.  49)  is  very  closely  related 
to  the  radish,  and  those  who  can  grow  the  latter  should 
have  no  trouble  with  the  former.     There  are  early  turnips, 
25 


374 


ELEMENTARY    STUDIES   IN   BOTANY 


PIG.  48. —  Radish. 


sown  as  soon  as  the  ground  can  be  worked,  for  use  in  the 

late  spring  and  summer ;  and  late  turnips,  sown  very  late  and 
stored  for  winter  use.  In  the  home  garden, 
the  seeds  are  planted  in  rows  ten  to  twenty 
inches  apart,  and  afterwards  the  plants  are 
thinned  to  six  to  ten  inches  apart  in  the 
rows.  Turnips  are  such  hardy  plants 
that  they  require  no  special  care  in  culti- 
vation. 

Turnips,  however,  are  often  grown  as  a 
field  crop,  to  be  raised  on  a  larger  scale, 
either  for  the  market  or  for  feeding.  In 
this  case  the  rows  are  farther  apart  (about 
30  inches),  so  that  a  horse  may  be  used  in 
tilling  the  soil.  It  is  reported  that  some- 
times the  yield  of  turnips  reaches  10CO 
bushels  to  the  acre. 
82.  Beet.  —  The  beet  belongs  to  a  family  of  homely  weeds, 

known  as  the  goosefoot  family  (Chenopo- 

diacese),  and  about  its  only  useful  associate 

is   spinach.     The   inconspicuous    flowers 

occur  in  clusters  which  form  a  spike ;  but 

the  leaves  are  large  and  sometimes  purple 

tinged,  and  are  often  used  for  "  greens." 
Young  beets  form  an  important  early 

crop  of  the  market  gardens,  often  many 

acres  being  employed  in  their  cultivation. 

The  soil  needed  and   the  tillage  are  the 

same  as  for  other  root  crops.     The  first 

sowing  is  done  as  soon  as  the  soil  can 

be  worked,  and  the  usual  rows  (about  a 

foot  apart)  are  established,  followed  by    FIG.  49 —Turnip.— After 

,  i  BAILEY. 

the  usual  thinning  (to  about  six  inches 

apart).     Of  course  when  horse  cultivation  is  desirable,  the 

rows  must  be  farther  apart  (two  to  three  feet).     There  is  also 


VEGETABLES  375 

a  fall  crop,  for  winter  storage,  the  seed  for  which  is  sown  in 
June. 

83.  Sweet  potato.  —  This  is  a  root  crop  that  differs  in 
several  particulars  from  those  just  described.  Sweet  potatoes 
are  often  mistakenly  called  tubers.  The  ordinary  potato 
is  a  tuber,  that  is,  a  thickened  underground  stem ;  but  a 
sweet  potato  is  a  thickened  root,  and  is  not  a  tuber  any 
more  than  radishes,  and  turnips,  and  beets  are  tubers.  In 
these  three  plants  just  mentioned,  the  "  vegetable  "  is  the 
thickened  tap-root ;  while  sweet  potatoes  are  thickened  root 
branches. 

The  sweet  potato  is  a  morning-glory,  in  which  genus 
(Ipomcea)  there  are  many  showy  cultivated  plants.  The 
family  is  called  the  convolvulus  family  (Convolvulacese). 
The  sweet  potato  plant  is  a  trailing  vine  whose  branches  root 
at  the  joints  (Fig.  50),  or  it  may  be  cultivated  as  a  bushy 
plant.  The  potatoes  are  borne  close  together  under  the 
crown  of  the  plant,  that  is,  just  below  where  the  stem  merges 
into  the  root,  or  where  the  joints  "  strike  root."  Since  sweet 
potato  is  a  morning-glory,  there  should  be  no  difficulty 
in  recognizing  its 
conspicuous  funnel- 
shaped,  purple  flow- 
ers (Fig.  50).  The 
leaves  are  quite 
variable,  having  a 
general  triangular 
outline,  and  often 

i  FIG.  50.  —  Sweet  potato. 

heart-shaped  at  base. 

Sweet  potatoes  are  more  extensively  cultivated  in  the 
United  States  than  in  any  other  country,  the  annual  yield 
being  about  50  million  bushels.  They  need  a  warm,  sunny 
climate,  a  long  growing  season,  loose,  warm  soil,  and  plenty 
of  moisture.  These  conditions  are  found  in  our  southern 
states,  and  therefore  sweet  potatoes  as  a  commercial  crop  are 


376 


ELEMENTARY    STUDIES   IN   BOTANY 


grown  almost  exclusively  in  the  southern  states,  from  Vir- 
ginia around  to  Texas.  The  most  northern  state  in  which 
they  are  grown  on  a  large  scale  is  New 
Jersey;  and  fairly  large  crops  are  pro- 
duced in  Ohio,  Indiana,  Illinois,  and 
California. 

Propagation  is  by  means  of  sprouts  that 
develop  from  the  potatoes  when  they  are 
planted  in  propagating  beds  or  frames. 
These  root  sprouts  are  used  as  slips  or 
cuttings.  Sometimes  cuttings  are  also 
obtained  from  the  tips  of  fresh  runners. 
The  plant  is  very  sensitive  to  frost,  and 
there  is  often  great  loss  on  account  of 
planting  too  early.  The  sprouts  are  set  in 

r°WS   ab°Ut  f°UI>  feet    aai>t     the       kntS    in 


FIG.  51.-Sweet  potato, 

showing  the  charac-    each  row  being   about    18   inches   apart. 

ter  of  flower  and  leaf  .  .  . 

A  good  average  yield  is  said  to  range 
from  200  to  400  bushels  an  acre,  and  the  crop  is  harvested 
immediately  after  the  first  frost. 

Sweet  potatoes  are  often  raised  in 
the  northern  states  on  a  small  scale  as  a 
home  garden  crop.  In  this  case,  loose- 
ness and  warmth  of  soil  are  secured 
by  planting  the  slips  on  ridges  of  soil. 

84.  Parsnip  and  carrot.  —  These 
vegetables  are  the  thickened  tap-roots 
(Fig.  52)  of  two  plants  belonging  to  the 
parsley  family  (Umbellif  erse)  .  They 
are  introduced  here  not  so  much  on 
account  of  their  importance,  as  to 
illustrate  root  crops  from  another 
family  of  plants.  The  family  is  a  large 
one,  including,  along  with  parsnip  and  carrot,  such  well- 
known  forms  as  coriander,  fennel,  caraway,  hemlock,  and 


FIG.  52.  —  Carrot. 


VEGETABLES  377 

celery;  in  other  words,  vegetables,  aromatic  plants,  and 
poisonous  plants.  The  family  receives  its  name  from  its 
characteristic  flower-cluster  (umbel),  which  is  flat-topped, 
the  individual  small  flowers  or  groups  of  flowers  standing  on 
branches  (rays)  that  arise  from  a  common  point  and  spread 
like  the  rays  of  an  umbrella.  Wild  carrot,  with  its  umbels 
of  small  white  flowers,  is  one  of  our  bad  weeds;  while  wild 
parsnip,  with  its  umbels  of  small  yellow  flowers,  is  very 
common. 

The  cultivation  of  parsnips  and  carrots  is  in  general  the 
same  as  for  such  root  crops  as  turnips  and  beets,  but  they  are 
slow-growing  plants  and  it  is  a  long  time  between  the  sowing 
and  the  harvest. 

Bulbs 

85.  Onion.  —  The  best-known  edible  bulb  is  the  onion, 
probably  a  native  of  western  Asia  and  brought  into  cultiva- 
tion in  very  ancient  times.  Onions,  leeks,  and  garlic  belong 
to  one  genus  (Alliuni),  which  is  a  member  of  the  lily  family 
(Liliacea3).  Among  their  associates  in  the  family  are  such 
ornamental  plants  as  the  lilies,  tulips,  and  hyacinths,  and  the 
well-known  vegetable,  asparagus. 

The  necessary  soil  is  the  usual  good  garden  soil,  and 
thorough  cultivation  is  required.  Onions  are  very  hardy,  and 
in  the  northern  states  the  seeds  are  sown  or  the  bulbs  planted 
as  soon  as  the  ground  can  be  prepared  properly  in  the  spring  ; 
in  fact,  it  is  common  to  get  a  good  start  by  preparing  the 
ground  in  the  fall. 

The  seeds  are  small  and  do  not  germinate  quickly,  and 
great  care  has  to  be  taken  to  keep  the  beds  free  from  weeds, 
as  onions  cannot  stand  such  competition.  The  seeds  are 
sown  thickly  in  rows,  and  afterwards  the  young  plants  are 
thinned  out  so  as  to  be  properly  spaced. 

It  is  more  common  to  propagate  onions  by  "  sets,"  espe- 
cially for  early  onions,  and  sets  are  of  three  kinds :  (1)  "  top 


378 


ELEMENTARY    STUDIES   IN   BOTANY 


onions/'  which  mean  the  bulblets  that  appear  in  the  flower- 
clusters;  (2)  "  multipliers  "  or  "  potato  onions/'  which  mean 
the  separate  parts  or  cores  in  which  a  bulb  often  develops ; 
and  (3)  ordinary  bulbs  arrested  in  growth,  sometimes  called 
11  stunts."  The  top  onions  quickly  produce  young  bulbs, 
and  these  are  the  "  young  onions  "  that  appear  in  market. 
The  stunted  bulbs  are  produced  from  seeds,  by  sowing  very 
thickly  in  rather  poor  soil.  In  such  conditions  the  bulbs 
soon  reach  their  limit  of  growth  and  are  harvested,  kept  over 
winter,  and  planted  in  more  favorable  conditions  the  next 
spring. 

Leaves 

86.  Cabbage.  —  This  plant  has  been  very  long  in  cultiva- 
tion, and  grows  wild  on  the  sea-cliffs  of  western  and  southern 
Europe  (Fig.  53).  From  this  wild  plant,  such  different- 
looking  forms,  as  the  various 
cabbages,  cauliflower,  Brussels 
sprouts,  etc.,  have  been  derived 
(Figs.  54-60).  It  belongs  to  the 
mustard  family  (Crucifera?),  and 
its  well-known  associates  are 
enumerated  in  the  account  of 
the  radish  (p.  372). 

Cabbages  can  grow  in  almost 
any  kind  of  soil,  but  they  must 
have  plenty  of  food  and  water, 
though  not  an  oversupply  of  the 
latter.  Hot  and  dry  air  does  not 
prevent  growth,  but  it  does  pre- 
vent the  formation  of  "heads," 
which  are  merely  large  buds.  For  this  reason,  heads  do  not 
form  well  in  the  summer  weather  of  the  United  States,  and 
hence  in  the  north  seed-sowing  is  timed  to  avoid  "heading" 
in  hot  weather,  while  in  the  south  the  plants  are  grown  during 
the  winter  and  spring  months. 


FIG.  53.  —  The  wild  cabbage  growing 
on  a  cliff.  —  After  BAILEY. 


66 


379 


380  ELEMENTARY   STUDIES   IN   BOTANY 

The  earliest  varieties  develop  in  about  three  months  from 
seed,  and  the  later  varieties  extend  this  period  up  to  six  or 
seven  months.  The  seeds  are  sown  in  boxes  in  the  usual 
rows,  and  then  transplanted  into  the  permanent  bed.  If  they 
are  to  be  set  out  in  March,  the  seed  is  started  early  in  Feb- 
ruary. For  later  crops  the  seed  is  sown  out  of  doors  in  a  well- 
prepared  germination  bed,  which  is  repeatedly  raked  to  hold 
moisture  until  the  plants  are  removed  to  their  permanent 
place. 

87.  Lettuce.  —  This  is  the  most  popular  salad  vegetable 
and  grows  so  quickly  that  it  should  be  one  of  the  forms  used 
in  school  work.  It  belongs  to  the  largest  family  of  flowering 
plants  (Composite),  a  family  which  is  also  the  highest  in 
rank,  which  means  that  it  is  regarded  as  the  most  highly 
organized  family  in  the  plant  kingdom.  Some  of  the  familiar 
associates  of  lettuce  in  this  great  family  are  such  ornamental 
plants  as  golden-rods,  asters,  daisies,  sunflowers,  dahlias, 
and  chrysanthemums ;  such  weeds  as  ragweed,  cocklebur, 
thistle,  and  dandelion;  and  such  useful  plants  as  chicory 
and  artichoke. 

The  family  is  characterized  by  its  compact  head  of  flowers, 
which  is  thought  of  by  most  persons  as  a  single  flower  (Fig. 
61).  But  if  the  so-called  flower  of  dandelion  or  sunflower  be 
examined,  it  will  be  discovered  that  it  consists  of  numerous 
very  small  flowers  packed  together  upon  a  flat  disk  (receptacle) , 
and  the  whole  assemblage  of  flowers  surrounded  by  a  rosette 
of  small  leaves  (involucre) . 

There  are  two  general  types  of  lettuce  in  cultivation  : 
(1)  head  lettuce,  which  heads  up  like  cabbage,  and  (2)  loose 
lettuce.  The  latter  is  more  used  because  it  is  grown  more 
easily,  but  the  former  is  regarded  as  the  finer.  Since  the 
value  of  lettuce  depends  upon  its  freshness,  it  is  grown  almost 
universally  in  home  gardens,  and  a  very  small  area  yields 
enough  to  supply  a  family.  There  is  no  vegetable  grown  so 
easily  in  sufficient  quantity  in  city  backyards.  The  proper 


VEGETABLES 


381 


FIG.  61.  —  The  head  (so-called  "flower")  of  a  composite  (Arnica) :  A,  a  plant  showing 
an  open  head ;  B,  one  of  the  flowers  that  make  up  the  margin  of  the  head ;  C,  one 
of  the  flowers  that  make  up  the  center  (disk)  of  the  head.  —  After  HOFFMAN. 

thing  is  to  secure  as  long  a  succession  of  fresh  lettuce  as  pos- 
sible. In  early  spring,  about  when  the  grass  is  starting,  a 
suitable  area  should  be  spread  with  fine  manure,  and  then  the 
soil  pulverized  and  smoothed  over.  A  furrow  about  an  inch 


382  ELEMENTARY   STUDIES   IN   BOTANY 

deep  is  marked  in  the  fine  soil,  the  seeds  are  dropped  in 
(twenty-five  to  fifty  in  a  foot),  and  then  covered  with  fine 
and  pressed-down  soil.  In  fifteen  to  twenty  days  the  plants 
are  thinned  out,  leaving  eight  to  ten  in  a  foot ;  and  at  the 
same  time  a  second  row  is  planted.  About  twenty  days  later 
the  first  row  is  thinned  again,  so  that  the  plants  are  six  to 
twelve  inches  apart  (according  to  size) ;  the  second  now  re- 
ceives its  first  thinning ;  and  a  third  row  is  started.  Even 
a  fourth  row  may  be  started,  but  it  is  not  likely  to  do  very 
well  on  account  of  the  hot  weather. 

For  market  purposes,  the  plants  are  started  in  the  green- 
house in  February,  and  planted  out  of  doors  as  soon  as  the 
weather  will  permit.  A  large  industry  has  developed,  also, 
in  forcing  lettuce  under  glass  at  all  times  of  the  year,  so  that 
fresh  lettuce  can  always  be  obtained. 

88.  Celery.  —  Celery  is  cultivated  for  the  leaf  stalks 
(petioles),  which  are  blanched  and  made  tender.  It  is 
poorly  grown  if  it  is  greenish  and  tough.  Celery  belongs  to 
the  parsley  family  (Umbelliferse) ,  and  its  well-known  asso- 
ciates were  enumerated  in  connection  with  the  account  of 
parsnips  and  carrots  (p.  376). 

This  vegetable  is  in  such  extensive  use  and  requires  such 
special  treatment  that  it  has  come  to  be  cultivated  as  a  field 
crop  rather  than  as  a  home  garden  crop.  For  its  best  develop- 
ment it  requires  a  special  soil,  really  a  bog  soil,  but  it  can 
be  grown  well  on  clay  or  even  sandy  soils  if  they  are  enriched 
and  irrigated.  Although  this  is  a  market  garden  crop  rather 
than  a  home  garden  crop,  the  use  of  celery  is  so  universal  that 
some  information  as  to  its  culture  seems  desirable. 

The  seeds  are  sown  in  special  frames  of  various  kinds,  and 
germination  is  a  slow  process,  the  seedlings  being  ready  to 
transplant  in  about  three  months.  For  the  early  crop  in  the 
northern  states,  therefore,  the  seeds  are  started  in  January; 
and  for  the  late  crop  they  are  started  in  March.  The  seeds 
are  broadcast,  and  the  young  seedlings  are  transplanted  to 


VEGETABLES  383 

other  frames  and  spaced  two  to  three  inches  apart.  As  soon 
as  a  new  set  of  roots  and  leaves  are  put  out,  the  plants  are  set 
out  in  the  field  about  six  inches  apart  in  rows  three  to  four 
feet  apart. 

For  blanching  the  early  plants  boards  are  used,  which  are 
set  up  on  edge  beside  the  rows,  brought  together  at  the  top, 
and  held  by  cleats.  Late  celery  is  blanched  by  banking  the 
earth  against  the  plants,  the  banking  being  heightened  two 
or  three  times. 

Another  common  vegetable  cultivated  for  its  petioles  is 
rhubarb,  which  belongs  to  the  buckwheat  family  (Poly- 
gonaceae),  and  has  various  "  docks  "  for  its  near  relatives. 

Fruit 

89.  Tomato.  —  The  tomato  is  a  native  of  tropical  America, 
and  this  at  once  suggests  that  it  is  sensitive  to  frost  and  needs 
warm  and  sunny  soil  and  a  long  season.  The  fruit,  which  we 
use  as  a  vegetable,  is  really  a  berry,  like  currants  and  goose- 
berries. The  fruit  was  once  called  "  love-apple  "  and  was 
thought  to  be  poisonous,  but  now  it  is  very  extensively  culti- 
vated, and  in  North  America,  where  it  is  grown  more  exten- 
sively than  in  any  other  country,  it  has  reached  its  highest 
degree  of  perfection  in  desirable  varieties.  In  the  United 
States  it  is  grown  more  extensively  for  canning  than  any  other 
vegetable,  a  recent  report  stating  that  over  130  million  cans 
are  packed  each  year,  representing  the  cultivation  of  300,000 
acres.  The  leading  states  in  tomato-production  for  canning 
purposes  are  Maryland,  New  Jersey,  Indiana,  and  California. 

Tomato  is  a  member  of  the  nightshade  family  (Solanaceae), 
and  its  familiar  associates  are  enumerated  in  connection  with 
the  account  of  the  potato  (p.  370). 

Since  the  plants  are  very  sensitive  to  frost,  they  are  started 
in  hotbeds  and  transplanted  as  soon  as  the  danger  of  frost  has 
passed.  The  plants  are  set  four  to  five  feet  apart  each  way, 
and  in  garden-cultivation  they  are  usually  "  trained  "  to  keep 


384  ELEMENTARY    STUDIES   IN   BOTANY 

the  fruit  off  the  ground,  thus  securing  more  rapid  ripening  and 
larger  and  better-colored  fruit.  The  best  method  of  training 
is  to  support  a  single  stem  by  a  stake,  but  this  is  troublesome 
when  many  plants  are  grown.  The  same  general  results  may 
be  secured  by  allowing  the  plants  to  grow  over  an  inclined 
rack  or  trellis. 

90.  The  gourd  family.  —  This  is  a  notable  family  (Cucur- 
bitacea?)  for  containing  numerous  useful  forms,  whose  fruits 
are  used  either  as  fruits  or  vegetables,  but  usage  has  included 
them  all  among  vegetables.  One  genus  furnishes  the  cucum- 
ber and  muskmelon ;  another  the  watermelon ;  and  a  third 
the  pumpkin  and  squash.  They  are  all  tendril-bearing 
herbs,  with  large,  more  or  less  lobed  leaves,  and  rather  large 
axillary  flowers,  which  are  usually  yellow.  The  flowers  are 
of  two  kinds,  one  (staminate)  bearing  the  three  stamens,  the 
other  (pistillate)  bearing  the  pistil.  In  pumpkin,  squash,  and 
watermelon,  both  kinds  of  flowers  are  solitary  in  the  axils ; 
while  in  cucumber  and  muskmelon  the  staminate  flowers  are 
in  clusters. 

All  of  these  forms  thrive  best  in  good  soil,  such  as  is  suitable 
for  corn  and  wheat ;  they  are  all  sensitive  to  frost ;  and  the 
seeds  of  all  are  planted  in  "  hills."  This  method  of  planting 
is  distinct  from  "  drills  "  or  rows,  meaning  the  dropping  of 
four  to  six  (or  more)  seeds  in  a  single  pocket  of  soil,  the 
groups  of  seeds  being  four  to  six  feet  (or  even  eight  to  ten  feet) 
apart  each  way.  It  is  also  very  customary  to  put  some  well- 
rotted  manure  in  each  hill,  thus  forcing  the  young  plants  into 
vigorous  and  continuous  growth. 

Cucumber.  —  The  cucumber  is  a  native  of  southern  Asia, 
and  has  therefore  been  long  in  cultivation.  It  is  grown  both 
as  a  field  crop  and  a  garden  crop,  and  seeds  can  be  sown  in  the 
open  as  soon  as  danger  of  frost  has  passed,  and  the  crop 
develops  during  the  warm  months. 

Muskmelon.  —  This  plant  is  a  native  of  the  warmer  parts  of 
Asia.  This  means  that  it  is  a  tender  plant,  and  an  early 


VEGETABLES  385 

start  in  the  northern  states  must  be  secured  by  starting  seeds 
in  hotbeds ;  but  in  the  southern  states  they  may  be  sown  in 
the  open  field.  There  are  two  general  types  of  muskmelon 
cultivated :  (1)  those  with  furrowed  and  thick  rind,  called 
"  canteloupes  " ;  and  (2)  those  with  netted  and  softer  rind, 
called  "  nutmeg  melons."  Two  notable  races  of  nutmeg  mel- 
ons are  the  "Osage  melon,"  developed  in  Michigan,  and  the 
"  Rocky  Ford  melon,"  developed  in  Colorado.  The  canteloupe 
melons  have  a  longer  season,  but  the  nutmeg  melons  are 
most  commonly  grown  in  the  northern  states  in  home  gardens 
and  for  the  early  market.  New  Jersey  is  said  to  supply 
one-half  the  muskmelon  crop ;  and  the  southern  states 
cultivate  muskmelons  only  for  the  local  markets. 

Watermelon.  —  The  watermelon  is  a  native  of  tropical 
Africa  and  has  been  very  long  in  cultivation,  but  the  United 
States  now  produces  a  larger  crop  than  any  country  in  the 
world.  The  watermelon  develops  to  the  greatest  perfection 
in  the  soil  and  climate  of  the  southern  states,  Georgia  being 
particularly  noted  for  producing  the  bulk  of  the  crop  shipped 
to  the  northern  states  and  also  the  choicest  melons.  Of 
course  in  the  southern  states  watermelons  are  grown  as  a  field 
crop,  but  they  can  be  grown  readily  in  home  gardens.  The 
soil  must  be  such  that  the  plants  can  start  quickly  and  grow 
rapidly. 

Pumpkin  and  squash.  —  These  coarse  trailing  vines  grow 
best  in  corn  land,  and  are  often  grown  in  cornfields,  being 
planted  along  with  the  corn. 

Seeds 

91.  The  legumes.  —  Peas  and  beans  are  the  chief  represen- 
tatives of  the  legume  family  (Leguminosae)  whose  seeds  are 
used  as  vegetables.  Other  familiar  representatives  of  this 
family  are  enumerated  in  the  account  of  forage  plants  (p.  362. 
It  is  evident  that  since  peas  and  beans  are  legumes  they  do 
not  impoverish  soil,  so  far  as  its  nitrates  are  concerned,  but 


386  ELEMENTARY   STUDIES   IN   BOTANY 

can  obtain  their  own  nitrates  with  the  help  of  soil  bacteria ; 
but  this  does  not  mean  that  they  can  do  well  on  poor  soil. 

Peas.  —  The  cultivation  of  peas  is  extremely  old,  the  plant 
being  a  native  of  southern  Europe  and  Asia,  and  used  exten- 
sively by  the  most  ancient  races.  There  are  numerous 
varieties  of  garden  peas  and  field  peas,  but  there  are  two 
types  of  garden  peas  that  can  be  recognized  easily  :  (1)  those 
with  smooth  seeds,  which  are  earlier  and  hardier  varieties; 
and  (2)  those  with  wrinkled  seeds,  which  are  of  better  quality. 
Many  of  the  garden  varieties  need  poles  six  to  eight  feet 
high  ;  others  are  not  such  high  climbers  ;  while  still  others  are 
dwarfs  and  do  not  need  stakes.  The  method  of  planting  and 
cultivating  is  the  same  as  for  beans,  and  will  be  described  in 
the  next  paragraph. 

Beans.  —  There  are  many  kinds  of  beans,  but  the  ordinary 
beans  cultivated  in  this  country  are  probably  natives  of  trop- 
ical America.  The  two  types  in  ordinary  cultivation  are  the 
bush  beans,  which  are  field  beans,  and  the  pole  beans,  which 
are  garden  beans,  the  latter  demanding  more  fertile  soil  than 
the  former,  especially  the  best  of  all  the  pole  beans,  the  Lima 
bean.  In  the  cultivation  of  field  beans,  the  seeds  are  usually 
planted  in  rows  two  to  three  feet  apart,  with  the  plants  three 
to  six  inches  apart  in  each  row,  and  the  soil  is  kept  well  stirred 
between  the  rows.  In  the  case  of  pole  beans,  the  poles  are 
set  about  four  feet  apart  each  way  and  four  or  five  beans 
planted  around  each  pole,  and  the  soil  is  cultivated  frequently. 

Sweet  corn  is  also  a  notable  seed-vegetable,  which  has  been 
presented  in  connection  with  the  cereals  (p.  350). 


CHAPTER   IX 
FRUITS 

92.  The  families.  —  The  majority  of  our  cultivated  fruits 
belong  to  the  rose  family  (Rosacese),  whose  name  suggests 
the  general  character  of  its  flowers,  with  their  more  or  less 
showy  petals  and  numerous  stamens  (Fig.  62).  One  divi- 
sion of  the  family  includes  in  a  single  genus  (Prunus) 
peaches,  apricots,  plums,  and  cherries,  which  are  "  stone 
fruits  "  or  "  drupes."  In  this  kind  of  fruit  the  outer  part 
of  the  ovary  becomes  fleshy  and  the  inner  part  stony,  the 
seed  being  the  kernel  within  the  stone  ("  pit  ")  (Fig.  63). 
In  the  case  of  the  almond,  the  outer  layer  ripens  dry  instead 
of  fleshy  and  splits  off,  freeing  the  large  and  softish  stone, 
whose  kernel  (the  seed)  is  eaten. 

Another  division  of  the  family  includes  in  a  single  genus 
(Pyrus)  apples,  pears,  and  quinces,  whose  fruits  are  "  pomes." 
In  this  case  the  flesh  consists  of  the  thickened  calyx  tube 
which  becomes  consolidated  with  the  ovary  ("  core  ")  (Fig. 
64).  The  edible  part  of  the  fruit,  therefore,  is  the  calyx 
tube,  while  in  stone  fruits  it  is  the  ovary  wall. 

The  third  and  largest  division  of  the  family,  to  which  the 
roses  themselves  belong,  includes  strawberries,  raspberries, 
and  blackberries.  The  strawberry  is  really  a  fleshy  recep- 
tacle on  which  numerous  minute  pistils  (the  "  pits  ")  are 
borne  (Fig.  65) ;  wh'ile  raspberries  and  blackberries  are  clus- 
ters of  small  fruits  resembling  minute  stone  fruits.  In  the 
raspberry  the  cluster  of  fruits  slips  from  the  receptacle  like 
a  cap  (Fig.  66) ;  while  in  the  blackberry  the  cluster  and  the 
receptacle  become  fleshy  together. 

387 


388  ELEMENTARY    STUDIES   IN   BOTANY 

A  second  important  fruit-bearing  family  is  the  rue  family 
(Rutacea),  whose  genus  Citrus  includes  oranges,  lemons, 
and  grape-fruits.  The  genus  is  a  native  of  Asia,  but  these 
fruits  are  known  everywhere.  From  the  name  of  the  genus, 
this  group  of  fruits  is  usually  called  the  "  citrous  fruits." 


FIG.  62. —  Pear,  showing  a  branch  with  flowers  (A),  a  section  of  the  flower,  showing, 
how  the  calyx  and  ovary  grow  together  to  form  the  fruit  (B),  and  a  section  of  the 
fruit  (C),  showing  the  thickened  calyx  outside  and  the  ovary  or  "core"  within  (indi- 
cated by  the  dotted  outline).  —  After  WOSSIDLO. 

These  are  all  really  berries  with  a  leathery  rind,  a  berry 
being  an  ovary  that  becomes  pulpy  throughout  (as  currants, 
gooseberries,  grapes,  tomatoes). 

A  third  notable  fruit-bearing  family  is  the  vine  family 
(Vitaceffi),  for  it  includes  the  grapes.  The  habit  of  these 
woody  climbers,  with  their  tendrils,  broad  leaves,  and  clus- 
teis  of  small  but  fragrant  flowers,  is  probably  familiar  to  all, 


FRUITS  389 

for  more  kinds  of  grapes,  both  wild  and  cultivated,  grow  in 
North  America  than  in  any  other  country. 

93.  Classification.  —  The    most    useful    classification    of 
these  fruits,  for  it  groups  them  according  to  methods  of  cul- 
ture, is  as  follows  :    (1)  orchard  or  tree  fruits,  which  are  sub- 
divided into  pome  fruits  (apple,  pear,  quince),  stone  fruits 
(peach,   plum,   cherry),    and   citrous   fruits    (orange,  lemon, 
grape-fruit)  ;    (2)  vine  fruits  (grape)  ;    and  (3)  small  fruits 
(strawberries,  raspberries,  blackberries,  currants,  and  goose- 
berries). 

Orchard  Fruits 

94.  Orchards.  —  The  cultivation  of  orchard  fruits  is  prob- 
ably most  highly  developed  in  North  America.     A  genera- 
tion ago  an  orchard  in  connection  with  a  home  was  the 
usual  thing  ;    but  now  great  areas  are  under  cultivation  by 
professional  fruit-growers.     In   the  old   home  orchard    the 
trees  were  left  to  take  care  of  themselves,  so  that  the  fruit 
crops    were   uncertain   and   variable,   dependent   upon  the 
accident   of    soil   and   climate.      Now 

great  care  is  given  to  the  soil  and  to 
the  trees,  and  the  result  has  been  great 
increase  in  productiveness,  greater  uni- 
formity, and  finer  quality. 

In  establishing  an  orchard  the  soil  is 
prepared  as  thoroughly  as  for  any  other 
crop,  and  for  two  or  three  years  deep 

.         .  FIG.     63.  —  Section    of    a 

ploughing  is  practised.     This  puts  the        peach,  showing  PuiP  and 

•  i    .  j       r        •       i  TJ-          £  stone     formed     as     two 

SOll  in  gOOd  physical    Condition  for    re-  layers  of  the  ovary  wall, 


taining  water,  makes  the  soil  salts  more 
available,  and  assists  the  young  trees 

in  establishing  a  sufficiently  extensive  root  system.     After- 
wards there  is  frequent  light  tillage  early  in  the  season  ;  then 
often  a  cover-crop  (such  as  clover)  is  sown,  which  is  left  all 
winter  and  is  ploughed  under  in  the  spring. 
26 


390  ELEMENTARY    STUDIES   IN   BOTANY 

Pruning  has  also  come  to  be  a  fine  art,  and  when  done 
properly,  a  little  every  year,  there  is  a  larger  yield ;  and  when 
to  this  there  is  ad'ded  an  intelligent  thinning  of  the  develop- 
ing fruit,  the  quality  is  improved. 

95.  Apple.  —  The  apple  is  the  most  important  pome 
fruit,  having  been  cultivated  from  very  ancient  times.  It 
is  a  native  of  southwestern  Asia  and  adjacent  Europe,  but 
is  now  under  cultivation  in  all  countries.  All  of  the  differ- 
ent kinds  of  apples,  which  number  about  1000  on  sale  in 


;  * 


FIG.   64.  —  Longitudinal  and  cross-sections  of  apple,  showing  the  "five-celled"   ovary 
(core)  imbedded  in  the  fleshy  cup  of  the  calyx. 

any  year,  have  been  derived  from  two  wild  species,  one  of 
which  has  given  rise  to  the  ordinary  apples,  the  other  to  the 
crab  apples.  The  enormous  number  of  varieties  makes  it 
possible  to  select  for  each  area  those  best  adapted  for  it, 
and  this  information  is  perhaps  best  obtained  from  the  various 
state  horticultural  societies. 

In  the  United  States  and  Canada  there  are  several  notable 
areas  of  apple  cultivation,  and  new  ones  are  being  developed 
rapidly.  What  has  long  been  regarded  as  the  finest  apple 
region  in  productiveness,  quality,  and  good  keeping  is  the 
region  extending  from  the  Great  Lakes  eastward  to  Nova 


FRUITS 


391 


FIG.  65.  —  A  straw- 
berry, being  an  en- 
larged and  pulpy 
receptacle  bearing 
numerous  seed-like 
fruits  sunken  in 
small  pits.  —  After 
BAILEY. 


Scotia.  Other  notable  regions  are  in  Virginia,  in  Arkansas, 
in  various  parts  of  the  plains,  and  in  the  Pacific  states. 
More  apples  are  produced  in  North  America 
than  in  any  country  of  the  world,  a  good 
crop  for  the  United  States  and  Canada 
being  approximately  100,000,000  barrels. 

One  of  the  reasons  why  the  proper  care 
of  apple  orchards  has  been  so  much  neg- 
lected is  that  they  thrive  reasonably  well 
almost  anywhere.  The  best  land,  however, 
is  said  to  be  good  wheat  or  corn  land,  which 
means  a  clay  loam.  The  grafting  methods 
by  which  old  stocks  may  be  used  to  sup- 
port more  desirable  varieties  have  been 
described  (p.  330). 

96.  Pear.  —  The  pear  is  also  a  native  of 
Asia  and  Europe,  but  is  a  much  more  un- 
certain crop  than  the  apple.  It  flourishes  best  from  the 
New  England  states  to  the  Great  Lakes,  and  on  the  Pacific 
slope.  In  the  interior,  the  uncertainty  of  the  pear  crop  arises 
from  the  prevalence  of  a  disease  called  "  pear  blight,"  which 
blasts  the  branches,  and  which  spreads  so  rapidly  that  exten- 
sive orchards  may  be  destroyed.  In  the  south,  the  climate  is 

too  warm  for  the  best 
development  of  trees 
and  for  the  best  qual- 
ity of  fruit ;  while  in 
the  northern  prairie 
states  the  winters  are 
too  severe. 

There  are  many 
varieties,  but  those 
most  common  in  the 
markets  are  very  apt  to  be  the  various  races  of  Bartlett, 
Kieffer,  and  Seckel  pears.  The  pear  can  be  grafted  on 


FIG.  66.  —  A  raspberry,  showing  the  "cap"  of  small 
fruits  removed  from  the  receptacle.  —  After  BAILEY. 


392  ELEMENTARY    STUDIES    IN   BOTANY 

quince  stock  and  grown  as  a  dwarf.  These  "  dwarf  pears  " 
reach  the  bearing  stage  earlier  than  the  others  and  are  more 
easily  handled  in  all  the  necessary  operations,  but  they  require 
more  care  than  do  the  ordinary  trees. 

The  quince  needs  no  special  statement.  It  is  an  interest- 
ing and  peculiar  fruit,  but  there  is  no  large  or  increasing 
demand  for  it. 

97.  Peach.  —  The  peach  is  probably  the  most  highly  prized 
of  the  stone  fruits.  A  native  of  Asia,  its  cultivation  in  the 
United  States  is  always  attended  with  risk.  This  arises 
from  the  fact  that  it  is  a  very  early  bloomer,  and  being  sen- 
sitive to  frost,  the  flowers  and  buds  are  in  danger  of  being 
killed  by  a  late  frost.  This  risk  is  greater  in  the  south  tnan 
in  the  north,  because  the  buds  swell  earlier. 

On  account  of  this  danger  from  freezing,  the  commercial 
areas  of  peach  cultivation  are  near  large  bodies  of  water, 
where  the  winter  temperature  is  milder,  as  near  the  sea- 
coast,  far  enough  inland  to  escape  strong  winds,  and  near 
the  Great  Lakes.  Of  course  peaches  are  grown  over  a  great 
range  of  country,  the  failures  probably  being  as  frequent  as 
the  successes,  but  the  commercial  regions  are  not  numerous. 

The  peach  orchards  along  the  southern  borders  of  the 
Great  Lakes  extend  along  Lake  Ontario  in  New  York  and 
Canada,  along  Lake  Erie  in  Ohio,  and  along  the  eastern 
shore  of  Lake  Michigan.  It  is  in  the  "  Michigan  fruit  belt  " 
that  the  peach  reaches  its  northern  limit  in  the  eastern  states. 

Another  large  area  extends  from  Connecticut,  near  Long 
Island  Sound,  southward  to  Cape  Charles  (Virginia),  the 
"  Delaware  peaches  "  holding  the  same  important  position 
in  the  eastern  market  that  the  "  Michigan  peaches  "  do  in 
the  western. 

Other  peach  areas  are  in  northern  Georgia  and  Alabama 
and  adjacent  states;  from  southern  Illinois  westward  into 
Kansas ;  in  western  Colorado ;  and  throughout  California, 
except  in  the  mountains. 


FRUITS  393 

As  may  be  inferred  from  the  regions  of  most  successful 
peach-cultivation,  a  light  and  sandy  soil  is  the  best,  being 
quite  in  contrast  with  the  best  soil  for  pome  fruits.  Peaches 
are  propagated  by  seeds,  and  then  on  the  seedlings  of  the 
first  year  the  desired  varieties  are  budded.  The  tilling  and 
other  care  of  a  peach  orchard  can  never  be  neglected. 

98.  Plum.  —  There  are  native  plums  in  all  countries,  and 
numerous   species   are   in   cultivation.     Since   they   are   so 
variable  in  origin,  they  are  not  equally  adapted  to  all  regions. 
The  European  type  is  the  plum  of  history  and  is  cultivated 
in  the  northeastern  states  and  on  the  Pacific  slope.     It  has 
produced  the  more  familiar  old  races,  such  as  the  Green 
Gage,  Damson,  etc.,  and  is  the  chief  source  of  prunes.     In 
the  same  regions,  and  also  in  parts  of  the  interior  and  in  the 
south,  the  Japanese  plums  are  gaining  recognition.     In  the 
colder  northern  regions  and  over  the  larger  part  of  the  in- 
terior basin  our  own  native  plums  are  cultivated.     There  are 
hundreds  of  varieties,  no  less  than  300  varieties  having  been 
derived  from  six  native  American  species. 

In  propagation,  grafting  and  budding  are  practised  as 
usual ;  but  to  secure  desirable  varieties  not  adapted  to  the 
soil  conditions  of  a  region,  it  is  customary  to  grow  stock 
plants  for  soil  conditions  and  graft  scions  upon  them  for  the 
fruit. 

Prunes  are  plums  that  dry  sweet  without  removing  the 
pits.  In  other  plums  there  is  a  fermentation  or  "  souring  " 
about  the  pit  as  the  plum  dries.  In  California,  prunes  form 
the  most  important  plum  product,  6,000,000  trees  (55,000 
acres)  being  reported  in  1900,  seven-eighths  of  which  were 
used  for  prune-production. 

99.  Apricot.  —  This    fruit,    intermediate    between    peach 
and  plum,  is  a  native  of  the  China-Japan  region,  and  is 
grown  commercially  in  New  York  and  other  eastern  states, 
and  also  in  California.     Its  importance  in  California  may  be 
indicated  by  the  fact  that  in   1900  there  were  3,000,000 


394  ELEMENTARY   STUDIES   IN   BOTANY 

trees  (40,000  acres)  in  cultivation,  and  the  acreage  was 
rapidly  increasing.  The  clanger  from  frost  is  the  same  as 
for  peaches,  but  the  interior  valleys  of  California  furnish  a 
most  congenial  situation. 

100.  Cherry.  —  The  cherry  is  of  European  origin,  and  the 
various  cultivated  races  are  grouped  as  sour  cherries  and 
sweet  cherries.     The  sour  cherries  are  cultivated  in  orchards 
for  canning  purposes  in  a  number  of  states,  extending  from 
New  York  and  New  Jersey  to  Kansas  and  Nebraska.     The 
sweet  cherries  are  restricted  mostly  to  what  is  called  "  door- 
yard  "  planting.     In  California,  cherries  are  the  least  com- 
mercially important  of  the  temperate  fruits,  but  they  attain 
unusual  size.     Cherry  trees  are  grafted  with  unusual  readi- 
ness, so  that  large  orchards  can  be  transformed  into  more 
desirable  varieties. 

101.  Orange. — This    is    the    best    known    of   the    table 
citrous  fruits,  and  is  one  of  the  oldest  of  cultivated  fruits. 
In  fact,  it  has  been  so  long  in  cultivation  that  its  native 
region   is  in  doubt,   although  probably  it   has  come  from 
southern  and  eastern  Asia.     Now  it  is  grown  in  all  warm 
temperate  and  tropical  countries. 

The  structure  of  an  orange  is  familiar  to  every  one,  but 
certain  variations  should  be  noted.  Ordinarily  an  orange 
contains  ten  compartments,  but  the  number  is  often  in- 
creased through  cultivation ;  and  in  some  cases  a  secondary 
axis  with  its  small  compartments  is  developed  in  the  center 
of  the  fruit,  forming  the  "  navel  "  orange.  The  best-known 
navel  orange  is  the  "  Washington  navel,"  which  started  as  a 
chance  seedling  brought  from  Brazil  in  1870.  This  navel 
orange  is  also  seedless. 

There  are  three  well-developed  orange  regions  in  the 
United  States  :  (1)  central  and  southern  Florida,  (2)  the  delta 
region  of  the  Mississippi,  and  (3)  California.  Formerly 
most  of  our  oranges  were  imported  from  the  Mediterranean 
region,  but  these  were  replaced  for  the  most  part  by  Florida 


FRUITS  395 

oranges.  In  the  winter  of  1894-1895,  however,  there  occurred 
the  "  great  freeze  "  in  Florida,  and  since  that  time  Cali- 
fornia oranges  have  become  better  known.  Some  apprecia- 
tion of  the  destruction  wrought  by  the  great  freeze  may  be 
obtained  from  the  statement  that  in  the  season  of  the  freeze 
the  orange  crop  of  Florida  had  reached  its  maximum,  6,000,000 
boxes,  while  in  the  next  year  there  were  only  100,000  boxes ; 
in  1900  the  crop  reached  1,000,000  boxes.  In  California,  in 
1900,  there  were  3,500,000  trees  in  cultivation  (nearly  one- 
half  of  them  bearing),  which  yielded  4,000,000  boxes  or  more. 
In  1911  the  citrous  crop  of  California  reached  a  total  of 
14,000,000  boxes. 

102.  Lemon.  —  This  is  one  of  our  most  important  com- 
mercial fruits,  and  is  cultivated  extensively  in  all  tropical 
and  subtropical  regions,  being  less  hardy  than  the  orange. 
In  our  country,   lemon  culture  is  practically  restricted  to 
Florida  and  California,  and  large  quantities  of  lemons  are 
imported,  chiefly  from  Italy  and  Sicily.     Lemon  culture  in 
Florida  was  almost  annihilated  by  the  cold  winter  of  1894- 
1895,  when  nearly  all  the  trees  were  killed,  leaving  only  a 
few  isolated  orchards  which  recovered.     Since  that  time, 
more  attention  has  been  given  to  other  fruits. 

In  California,  although  the  lemon  has  been  grown  for  a 
long  time,  its  commercial  importance  has  increased  only 
in  comparatively  recent  times.  In  1900  there  were  250,000 
bearing  trees  and  a  million  more  in  cultivation.  The 
prominence  of  California  lemons  has  come  from  the  fact 
that  the  old  thick-skinned,  bitter,  and  rather  juiceless  type 
has  been  replaced  by  types  having  the  thin  rind,  freedom  from 
bitterness,  and  abundance  of  citric  acid  characteristic  of 
the  lemons  of  the  Mediterranean  region. 

103.  Grape-fruit.  —  This  citrous  fruit  has  come  into  great 
prominence,  and  there  have  been  many  misconceptions  as  to 
its  origin.     It  is  a  native  of  the  Malayan  and  Polynesian 
Islands  and  its  real  name  is  "  pomelo,"  a  name  which  means 


396  ELEMENTARY   STUDIES   IN   BOTANY 

literally  "  melon  apple."  When  it  came  into  cultivation  in 
Jamaica  it  was  called  "  grape-fruit  "  because  the  fruit  is 
borne  in  clusters  of  three  to  fifteen,  like  a  cluster  of  huge 
grapes.  It  has  also  been  called  "  fruit  of  Paradise  "  and 
"  forbidden  fruit/'  and  the  pear-shaped  varieties,  which  now 
seldom  appear  in  market,  are  called  "  shaddocks." 

Grape-fruits  are  cultivated  extensively  in  India,  the  West 
Indies,  Florida,  and  California,  but  most  of  the  cultivated 
varieties  have  been  developed  in  Florida,  where  it  is  grown 
to  greatest  perfection.  Its  commercial  cultivation  extended 
from  Florida  to  Jamaica  and  California.  The  grape-fruit  is 
cultivated  like  the  orange,  but  it  is  more  sensitive  to  cold, 
and  in  the  destructive  winter  of  1894-1895  all  the  trees  were 
killed  in  northern  and  central  Florida. 

Vine  Fruits 

104.  Grape.  —  The  grape  is  probably  the  oldest  fruit  in 
cultivation,  and  its  chief  use  has  been  the  manufacture  of 
wine.  The  grape  of  history  is  Vitis  vinifera  (the  specific 
name  means  "  wine-bearing  "),  and  it  is  probably  of  Asiatic 
origin.  Although  the  chief  use  of  grapes  is  to  manufacture 
wine,  a  secondary  use  is  the  production  of  raisins,  and  in 
the  United  States  there  has  been  developed  a  notable  series 
of  "  table  grapes." 

The  grape  in  this  country  has  had  a  most  interesting  his- 
tory. The  early  settlers  naturally  tried  to  introduce  the 
European  Vitis  vinifera,  but  after  persistent  effort  its  cul- 
tivation had  to  be  abandoned  on  account  of  a  destructive 
disease  that  attacked  it.  Then  attention  was  given  to  the 
possibilities  of  the  native  American  grapes,  of  which  there 
are  numerous  species.  A  species  of  the  Atlantic  coast 
region  (Vitis  Labrusca)  has  been  most  developed,  and  its 
cultivated  varieties  were  produced  to  eat  rather  than  to 
drink.  Among  them  are  such  well-known  grapes  as  the 
Concord  and  Catawba.  The  United  States  is  responsible, 


FRUITS  397 

therefore,  for  the  development  of  the  highest  types  of  table 
grapes.  In  addition  to  the  native  species  that  have  been 
brought  under  cultivation,  from  which  800  named  varieties 
have  been  produced,  there  are  numerous  other  promising 
species  that  await  development.  While  table  grapes  were 
being  developed  in  the  eastern  states,  the  Old  .World  Vitis 
vimfera  was  being  established  in  California,  where  it  was 
free  from  the  disease  which  attacked  it  in  the  eastern  spates. 
In  California,  therefore,  grape  culture  is  like  that  in  Europe, 
and  wine  is  the  principal  product. 

Although  grapes  are  cultivated  almost  everywhere  in 
the  United  States,  the  area  of  commercial  grape  culture  is 
not  very  extensive.  The  greatest  areas  in  the  eastern 
states  are  those  in  New  York  and  Ohio  bordering  lakes  and 
large  streams,  as  the  lower  part  of  the  Hudson  River  valley, 
the  lake  region  of  central  and  western  New  York,  and  the 
Lake  Erie  region  of  New  York,  Pennsylvania,  and  Ohio. 
There  are  also  large  vineyards  in  Ontario,  Michigan,  etc., 
and  grape  culture  is  extending  into  other  regions.  The 
area  of  grape  culture  in  California  in  1900  was  140,000  acres, 
one-seventh  of  the  product  being  table  grapes,  two-sevenths 
raisin  grapes,  and  four-sevenths  wine  grapes. 

The  care  of  grape-vines  requires  knowledge  and  experi- 
ence, for  proper  pruning,  to  reduce  the  amount  of  wood  and 
to  keep  the  plant  in  suitable  form,  can  be  learned  only  by 
demonstration.  The  training  of  the  vines  is  to  keep  them 
off  the  ground,  so  that  the  fruit  may  be  exposed  to  light  and 
air.  Naturally  in  extensive  cultivation  this  training  is  of 
the  simplest  sort  to  secure  the  result ;  but  in  home  cultiva- 
tion it  often  takes  the  form  of  a  more  or  less  elaborate  "  grape 
arbor."  The  propagation  of  grapes  is  usually  by  cuttings, 
already  described  (p.  326),  which  are  usually  secured  in  the 
winter  from  the  trimmings  of  vineyards.  These  cuttings, 
each  one  with  two  or  three  buds,  are  usually  kept  until  spring 
by  being  buried  half  their  depth  in  sand  in  a  cellar. 


398  ELEMENTARY    STUDIES   IN   BOTANY 

Small  Fruits 

105.  Strawberry.  —  There  are  wild  strawberries  in  the 
eastern  states,  and  a  generation  or  two  ago  strawberries 
were  scarcely  known  except  in  the  wild  state,  but  these  wild 
species  have  not  yielded  much  to  .cultivation.  All  of  the 
common  cultivated  forms  are  derived  from  a  Pacific  coast 
species  which  was  introduced  into  cultivation  over  200 
years  ago  from  Chili.  It  is  now  possible  for  any  one  who 
has  a  plot  of  ground  to  have  a  strawberry  bed. 

The  strawberry  plant  is  propagated 
naturally  by  runners,  which  form  after 
blossoming.  A  runner  strikes  root  at  the 


FIG.  67.  —  A  strawberry  plant,  showing  a  runner  that  has  de- 
veloped a  new  plant,  which  in  turn  has  sent  out  another  runner. 
—  After  SEUBERT. 

tip  and  sends  up  a  cluster  of  leaves,  thus  establishing  an  inde- 
pendent plant  (Fig.  67).  In  cultivation,  these  runner  plants 
are  transplanted  or  let  alone,  and  they  bear  fruit  the  follow- 
ing year.  A  strawberry  bed  may  bear  for  several  years, 
but  the  first  and  second  crops  are  the  best,  so  that  it  is  cus- 
tomary to  break  up  a  bed  after  one  to  three  years  of  bearing. 
The  best  soil  is  a  dark,  sandy,  and  rather  moist  loam,  and 
good  drainage  is  necessary.  In  preparing  a  bed  the  soil  is 
top-dressed  with  fine  manure  and  well  pulverized.  Then 
the  plants  are  set  out,  obtained  from  the  runner  plants  of  the 
previous  season.  These  young  plants  are  usually  better 
allowed  to  remain  in  connection  wTith  the  parent  plants  until 


FRUITS  399 

spring  and  then  transplanted,  and  of  course  runner  plants 
that  have  not  borne  fruit  are  the  best.  To  secure  the  best 
berries,  each  plant  should  have  a  space  to  itself  ("  hill  "), 
which  can  be  cultivated  all  around.  The  old  way  of  allow- 
ing beds  to  become  matted  with  runners  is  passing  out,  for 
many  berries  are  covered  up  and  in  a  very  unfavorable  posi- 
tion for  development.  Therefore,  when  a  large  area  is  under 
cultivation,  and  liberal  hills  are  impracticable,  narrow  and 
rather  close  rows  are  used,  so  that  as  much  fruit  as  possible 
may  be  "on  the  outside."  In  the  fall  it  is  usual  to  mulch 
the  beds  to  protect  them  through  the  winter  and  early 
spring.  This  mulch  is  a  covering  of  clean  straw  or  material 
containing  straw.  In  the  south,  pine  needles  are  used,  while 
near  the  sea-coast  salt  marsh  hay  is  convenient. 

The  growth  of  strawberry  plants  is  during  the  cool  season 
of  the  year,  and  of  course  in  the  south  this  means  very  early 
in  the  year.  In  fact  the  cultivated  berries  seem  to  find  their 
most  congenial  home  in  the  south,  where  they  are  the  most 
important  of  the  small  fruits. 

106.  Raspberry.  —  Raspberries  are  brambles,  associated 
in  the  same  genus  (Rubus)  with  blackberries,  from  which 
they  differ  in  the  fact  that  the  close  cluster  of  small  fruits 
separates  from  the  receptacle  like  a  cap.  The  European 
species  (Rubus  Idceus)  has  been  longest  in  cultivation,  and 
has  yielded  many  important  varieties  of  high  quality,  but 
it  lacks  hardiness  and  productiveness  in  the  United  States, 
and  for  this  reason  it  is  our  least  important  species. 

It  is  from  American  species  that  we  have  obtained  our 
commonly  cultivated  red  and  black  raspberries.  Rubus 
strigosus  is  a  red  raspberry,  like  its  European  relative.  Per- 
haps it  is  inferior  in  quality,  but  it  is  more  hardy  and  pro- 
ductive, and  therefore  almost  all  the  red  raspberries  of  the 
market  are  from  this  American  species.  Rubus  occidentalis  is 
the  black  raspberry,  or  "  black  cap,"  and  its  races,  although 
they  are  perhaps  less  liked  by  most  people  than  the  reds,  are 


400  ELEMENTARY    STUDIES   IN   BOTANY 

our  most  important  commercial  raspberries,  for  they  are 
easily  cultivated,  are  hardy  and  productive,  and  are  better 
for  market  handling.  The  black  raspberries  are  propagated 
by  cuttings  obtained  by  layering,  a  process  already  described 
(p.  329)  ;  while  red  raspberries  develop  numerous  suckers 
from  the  roots  which  are  often  used  as  cuttings. 

107.  Currant  and  gooseberry.  —  These   are  two   of  our 
hardiest  bush  fruits,  that  are  propagated  by  cuttings,  layer- 
ing,  and  root  cuttings.     They  are  more  intensively  culti- 
vated in  England  than  in  the  United  States,  the  English 
gooseberries  being  highly  cultivated  and  used  as  a  table  fruit 
in  a  way  that  is  impossible  with  their  American  relatives. 

108.  Suggestions  for  work.  —  The   fruits   mentioned   in 
this  chapter  are  in  such  common  use  and  so  easily  recognized 
that  there  is  no  need  for  exercises  in  distinguishing  them,  but 
there  are  four  useful  things  that  should  be  done  if  possible. 

1.  The  various  fruits  should  be  sectioned  and  their  struc- 
ture examined,  noting  the  variations  that  occur,  especially 
in  the  amount  of  fruit  pulp. 

2.  The  home  markets  should  be  visited  and  inquiries  made 
as  to  the  sources  of  the  fruit  displayed.     This  will  develop 
some  knowledge  of  the  regions  from  which  various  fruits  come 
at  different  seasons,  and  will  also  fix  the  seasons  when  the  dif- 
ferent fruits  may  be  expected  and  when  they  are  at  their  best. 

3.  The  names  of  the  most  common  varieties  should  be 
learned.     For    example,    the    prominent    apples    and    pears 
should  be  known  by  name  and  recognized  at  sight. 

4.  If  the  neighborhood  permits   it,   orchards,   and   even 
dooryards  and  gardens,  should  be  visited  to  see  the  various 
fruit-bearing  plants  in  cultivation.     This  will  fix  in  mind 
the  general  habit  of  the  plants,  their  appearance  in  cultiva- 
tion, and  will  probably  enable  the  student  to  contrast  proper 
and  improper  methods  of  cultivation. 


CHAPTER  X 
FLOWERS 

109.  Floriculture.  —  The  cultivation  of  flowers  for  orna- 
ment and  of  ornamental  plants  is  called  floriculture.  The 
use  of  plants  for  this  purpose  has  brought  into  cultivation  a 
very  large  number  of  species ;  in  fact,  floriculture  has  drawn 
upon  the  whole  of  the  immense  group  of  flowering  plants 
( Angiosperms) ,  and  has  selected  for  its  work  whatever  is 
beautiful  or  curious.  It  is  evident  that  it  will  be  impossible 
to  give  an  account  of  even  the  most  common  flowers  and 
ornamental  plants  in  cultivation,  but  some  general  idea  can 
be  given  of  the  work  of  floriculture.  Plants  are  in  more 
general  cultivation  for  their  flowers  than  for  any  other  pur- 
pose. The  public  parks  are  full  of  them,  almost  every  yard 
has  its  flower  bed,  and  in  the  absence  of  yards  "  window- 
gardens  "  are  established.  The  cultivation  of  such  plants, 
therefore,  touches  the  experience  of  more  people  than  any 
other  kind  of  cultivation;  besides,  it  is  just  as  possible  in 
cities  as  in  the  country. 

Floriculture  is  not  merely  the  cultivation  of  ornamental 
plants  by  people  in  general,  but  it  has  also  developed  into 
an  extensive  business,  conducted  by  "  florists,"  and  the 
work  is  done  chiefly  in  greenhouses.  The  demand  for  flowers, 
and  especially  "  cut  flowers,"  has  been  increasing  at  such  a 
rate  that  special  equipment  for  forcing  flowers  and  distribut- 
ing them  has  been  developed.  Naturally  the  largest  estab- 
lishments are  near  the  large  cities,  where  the  demand  is 
greatest,  and  the  cities  which  are  now  leading  in  this  busi- 
ness are  New  York,  Chicago,  Boston,  and  Philadelphia. 
The  greatest  amount  of  greenhouse  space  used  for  floricul- 

401 


402  ELEMENTARY   STUDIES   IN   BOTANY 

ture  is  found  in  New  York,  Illinois,  Pennsylvania,  and  New 
Jersey,  in  the  order  named.  It  is  reported  that  about 
$25,000,000  are  expended  for  flowers  each  year,  about  half 
of  it  for  cut  flowers  and  the  other  half  for  plants. 

The  most  important  commercial  flower  grown  is  the  rose, 
the  annual  sale  being  at  least  $6,000,000,  which  represents 
about  one  billion  flowers.  The  second  flower  in  importance 
is  the  carnation,  the  annual  sale  being  about  $4,000,000; 
while  the  violet  is  the  third. 

A  brief  account  will  be  given  of  the  cultivation  of  a  few 
representative  flowers,  and  they  will  serve  to  illustrate  the 
cultivation  of  flowers  in  general. 

110.  Production  of  new  forms.  —  Great  attention  is  given 
by  florists  to  the  production  of  new  forms  of  flowers  which 
may  attract  attention.  Every  year  new  forms  of  roses, 
carnations,  chrysanthemums,  etc.,  are  announced.  Some 
of  these  variations  are  obtained  by  detecting  a  chance  varia- 
tion or  "  sport  "  occurring  among  the  ordinary  plants.  Far 
the  greater  number,  however,  are  deliberately  worked  for 
by  hybridizing  (p.  338).  Two  forms  are  selected  and  arti- 
ficial pollination  is  secured.  The  hybrid  progeny  from  the 
seeds  are  examined  in  the  hope  that  one  or  more  individuals 
may  show  desirable  characters,  either  new  characters  or  a 
new  combination  of  characters,  and  these  are  propagated. 
Repeated  crosses  may  be  made,  several  varieties  being  used 
and  hybrids  being  crossed  again,  until  often  very  complex 
mixtures  are  obtained.  It  is  evident  that  by  making  crosses 
repeatedly  and  in  every  direction,  a  reasonable  number  of 
attractive  combinations  are  obtained.  It  is  like  stirring  up 
all  sorts  of  food  ingredients  in  all  sorts  of  proportions,  in  the 
hope  that  some  one  of  the  mixtures  will  prove  to  be  a  pala- 
table dish.  While  this  method  of  securing  new  forms  seems 
to  be  largely  a  matter  of  chance,  if  a  sufficiently  large  number 
of  hybrid  forms  is  produced,  the  chance  of  securing  a  desir- 
able form  becomes  a  practical  certainty. 


FLOWERS  403 

It  must  not  be  supposed  that  miscellaneous  mixtures  are 
the  only  ones  used  by  florists.  Often  the  mixtures  are 
definite  and  have  in  view  a  combination  of  desirable  char- 
acters that  exist  separately  in  the  two  parents.  For  example, 
it  is  very  common  to  work  for  such  a  combination  as  color 
and  size  of  flower,  by  crossing  flowers  of  the  desired  color 
with  flowers  of  the  desired  size.  In  this  way,  for  example, 
many  new  carnations  and  chrysanthemums  are  produced. 
Often  it  is  desired  merely  to  increase  the  size  of  a  desirable 
flower  beyond  its  usual  limit,  and  this  can  usually  be  secured 
by  the  selection  and  propagation  of  the  largest  flowers 
through  a  series  of  generations.  This  has  resulted  in  the 
production  of  some  remarkably  large  chrysanthemums  and 
carnations. 

One  of  the  best  illustrations  of  crossing  to  secure  definite 
results  is  the  Shasta  daisy  produced  by  Luther  Burbank. 
It  is  a  triple  hybrid,  that  is,  it  is  a  mixture  of  three  forms, 
each  one  contributing  certain  features.  The  American  form, 
common  throughout  the  east  as  a  weed,  is  known  as  oxeye 
daisy  or  marguerite.  It  is  an  abundant  bloomer,  but  the 
habit  of  the  plant  is  not  handsome,  being  rather  loose  and 
straggling.  The  English  representative  has  a  handsome 
habit,  with  tall  and  stiff  stems;  while  the  Japanese  form 
is  characterized  by  the  pearly  luster  of  the  flowers.  By 
crossing  these  three  forms,  the  Shasta  daisy  was  produced, 
which  combines  in  a  single  individual  the  profuse  blooming 
of  the  American  form,  the  erect  habit  of  the  English  form, 
and  the  pearly  white  flowers  of  the  Japanese  form. 

Ill .  Rose.  —  The  varieties  of  roses  (Fig.  68)  are  so  numer- 
ous and  the  methods  of  handling  them  are  so  varied  that  no 
general  account  can  cover  them.  The  situation  may  be 
illustrated,  however,  by  taking  the  case  of  a  home  rose 
garden,  which  any  one  can  secure  who  controls  a  small  plot 
of  ground. 

The  spot  selected  must  be  sunny,  but  protected  against 


404 


ELEMENTARY    STUDIES   IN   BOTANY 


the  worst  winds,  as  by  a  fence  or  hedge.  As  a  well-known 
writer  has  said,  "  the  rose  garden  must  have  shelter,  but  it 
must  not  have  shade."  The  best  results  are  secured  with 
good  garden  soil,  but  a  rose  bed  can  be  made  good  if  the 
original  soil  is  bad,  the  chief  thing  to  provide  for  in  such  a 
case  being  a  deep  bed  and  good  drainage,  for  roses  do  not 
tolerate  free  water  in  the  soil.  Roses  are  propagated  by 
seeds,  cuttings,  grafting,  and  budding,  but  those  who  are 
preparing  a  small  rose  garden  will  probably  use  cuttings  or 

started  plants  obtained  from 
a  florist  or  from  a  neighbor. 
These  cuttings  are  best  planted 
late  in  autumn,  about  30  inches 
apart,  and  the  soil  protected, 
preferably  with  stable  manure. 
In  the  spring  the  bed  should 
receive  shallow  tillage,  and  then 
the  surface  should  be  raked  at 
intervals. 

Cultivated  roses  are  roughly 
grouped  into  two  kinds :  those 
that  bloom  only  once  (in  sum- 
mer) and  those  that  bloom  more 

or  less  continuously.  The  varieties  are  so  numerous,  how- 
ever, and  differ  so  much  as  to  hardiness  and  adaptation  to 
different  regions,  that  advice  as  to  the  selection  of  the 
proper  forms  to  cultivate  must  be  obtained  from  those  who 
have  had  experience. 

112.  Carnation.  —  Carnations  (Fig.  69)  belong  to  the  pink 
family  (Caryophyllacese),  and  are  associated  in  the  same 
genus  (Dianthus)  with  the  old-fashioned  and  fragrant 
"  pinks  "  once  found  in  every  home  garden.  The  cultivated 
carnations  are  derived  from  a  European  species  (Dianthus 
Caryophyllus),  which  has  been  cultivated  from  very  early 
times.  The  name  "  carnation  "  was  applied  to  the  plant 


FIG.  68.  —  A  rose.  —  After  BAILEY. 


FLOWERS 


405 


on  account  of  its  flesh-colored  flowers,  but  the  color  of  the 
flower  in  its  wild  state  has  been  broken  up  into  a  great 
variety  of  colors  in  the  cultivated  races.  It  may  be  of 
interest  to  know  that  the  old  English  name  for  carnation 
was  "  gillyflower,"  a  name  that  appears  often  in  English 
literature. 

The  older  cultivated  races  of  carnations  have  practically 
disappeared,  and  have  been  replaced  .by  new  ones  that 
flower  more  or  less  continuously  and  are 
especially  adapted  for  forcing,  so  that  car- 
nations can  be  obtained  at  any  season  of 
the  year.  It  is  reported  that  about  500 
varieties  of  carnation  have  been  produced 
in  the  United  States,  where  the  carnation 
industry  is  better  developed  than  in  any 
other  country. 

Of  course  carnations  can  be  grown  from 
the  seed,  but  florists  use  this  method  only 
when  they  are  desirous  of  securing  varia- 
tions that  may  be  useful.  In  general,  they 
are  propagated  by  cuttings,  which  may 
seem  strange  for  an  herb.  Carnations  are 
not  very  suitable  for  ordinary  garden  cul- 
tivation, but  no  one  will  regret  the  culti- 
vation of  a  few  "  pinks  "  with  their  clove-like  fragrance. 

113.  Violet.  —  It  has  been  stated  that  violet  culture  is 
third  in  commercial  importance  among  cultivated  flowers. 
The  numerous  commercial  violets  are  derived  from  the 
European  Viola  odorata,  and  their  successful  cultivation  re- 
quires an  amount  of  intelligent  care  that  can  be  given  only 
by  the  specialist. 

If  the  violets  of  the  florists  are  not  suitable  for  home  cul- 
ture, another  violet,  the  pansy,  is  always  suitable,  for  it  is 
very  easy  to  cultivate  (Fig.  70).     The  pansies  are  derived 
from  another  European  species,  Viola  tricolor,  the  name  re- 
27 


FIG.  69. — A  carnation. 


406 


ELEMENTARY   STUDIES   IN   BOTANY 


FIG.  70.  —  Pansies. 


ferring  to  the  characteristic  variegated  colors  of  the  flower. 
The  old  English  name  of  the  pansy  is  "  heart 's-ease,"  and 

it  has  always  been  a  favorite 
home-garden  flower.  Numerous 
garden  varieties  have  been  devel- 
oped, '  that  differ  as  to  size  of 
flower,  nature  of  coloring,  and 
arrangement  of  colors.  The  highly 
developed  varieties  are  not  apt  to 
continue  true  in  unskilled  hands, 
so  that  the  safest  plan  is  to  secure 
seed  from  the  breeder  each  year. 

The  plot  selected  for  the  culti- 
vation of  pansies  should  be  shel- 
tered from  wind  and  exposed  to 
the  morning  sun  if  possible,  and 
good  garden  soil  will  produce  the  best  pansies.  For  early 
spring  blooming,  the  seed  is  sown  in  August,  the  bed  is  cov- 
ered with  strawy  manure  and  kept  moist. 
In  about  two  weeks  the  plants  will  ap- 
pear and  the  straw  is  gradually  removed. 
In  the  next  spring  the  flowers  will  appear. 
To  secure  blooming  during  the  late  sum- 
mer and  autumn,  seeds  can  be  germinated 
within  doors  from  February  to  June,  and 
the  young  plants  set  out  into  the  per- 
manent bed. 

114.  Sweet  pea.  —  Sweet  peas  (Fig. 
71),  as  the  name  suggests,  belong  to  the 
legume  family  (Legumiriosse),  along  with 
garden  peas  and  beans.  The  originals  of 
the  cultivated  varieties  came  from  the 
Mediterranean  region  and  southern  Asia, 
and  the  number  of  shades  of  color  now  represented  by  the 
200  varieties  is  surprising.  The  supply  of  seed  for  the  world 


FIG.  71.  —  Sweet  peas. 


FLOWERS 


407 


is  produced  principally  in  California,  and  on  this  account  a 
large  number  of  new  forms  have  been  secured  in  America. 

Although  the  cultivation  of  fancy  strains  has  been  made  a 
matter  of  competition,  the  sweet  pea  is  still  a  home-garden 
plant  and  is  usually  one  of  the  few  selected  for  planting. 
Garden  soil  is  needed,  but  it  must  be  remembered  that  too 
much  enriching  will  result  in  a  vigorous  vine  at  the  expense 
of  flowers.  The  soil  is  prepared  in  the  autumn,  and  the 
seeds  are  planted  as  soon  as  the  frost  is  out  of  the  ground. 
The  seeds  are  placed  in  rows  and  cov- 
ered so  that  a  little  furrow  is  left  for 
the  retention  of  moisture.  Germination 
and  early  growth  should  be  allowed  to 
proceed  slowly,  and  very  superficial  till- 
ing should  be  employed.  The  usual 
garden  varieties  need  a  firm  support  of 
some  kind,  about  six  feet  high ;  but 
there  are  bush  varieties  that  require  no 
support;  and  also  low  varieties  that 
spread  compactly  over  the  ground. 

115.  Chrysanthemum.  —  This  is  not 
an  ordinary  home-garden  plant  (Fig.  72), 
but  it  is  so  familiar  a  flower  and  has 
had  such  an  interesting  history  that  some  information  in 
reference  to  it  is  not  out  of  place.  It  belongs  to  the  com- 
posite family  (Compositse),  the  ranking  family  of  flowering 
plants,  associated  with  golden-rods,  asters,  sunflowers, 
dahlias,  dandelions,  etc.,  its  so-called  flower  being  a  compact 
head  of  small  flowers  surrounded  by  leafy  bracts  (involucre), 
as  described  under  lettuce  (p.  380). 

The  cultivated  chrysanthemum  holds  the  same  con- 
spicuous position  among  the  cultivated  flowers  of  the  orient 
that  the  rose  holds  in  the  Occident,  the  original  forms  growing 
as  natives  in  China  and  Japan.  There  are  very  many  types 
in  cultivation,  but  those  ordinarily  exhibited  have  large  and 


FIG.    72.  —  A  chrysanthe- 
mum. 


408 


ELEMENTARY   STUDIES   IN   BOTANY 


"  doubled  "  flowers  of  various  colors,  with  the  flowers  some- 
times in  a  compact  ball,  at  other  times  more  loosely  disposed. 
It  is  said  that  the  chrysanthemum  stands  fourth  in  the  list 
of  commercial  flowers  in  the  United  States,  although  its 
season  is  only  about  six  weeks  long. 

116.  Narcissus.  —  This  is  a  genus  of  the  amaryllis  family, 
which  includes  some  of  the  most  attractive  of  the  very  early 
home-garden  flowers.  They  are  known  in  general  as  daffo- 
dils and  jonquils,  and  are  familiar  to 
every  one.  The  flowers  are  charac- 
terized by  having  a  "  crown  "  aris- 
ing from  the  top  of  the  tubular, 
six-lobed  perianth.  The  daffodils 
have  large  yellow  flowers,  with  a 
crown  as  long  as  the  lobes  of  the 
flower  or  longer  and  with  a  more  or 
less  crisped  margin  (Fig.  73) ;  while 
the  jonquils  have  small  yellow  and 
fragrant  flowers,  with  a  crown  less 
than  half  the  length  of  the  flower 
lobes.  The  "  poet's  Narcissus," 
often  cultivated  and  seen  at  flor- 
ists, is  like  the  jonquil,  except  that 
the  fragrant  flowers  are  white  and 
the  short  crown  is  edged  with  pink. 

These  plants  are  hardy  and  easily  cared  for,  so  that  no 
garden  should  be  without  them.  They  thrive  in  good  soil, 
and  they  develop  so  early  that  moisture  is  usually  plentiful. 
About  the  only  caution  necessary  is  to  be  careful  that  no 
manure  touches  the  bulbs.  The  bulbs  are  planted,  late  in 
summer  or  early  in  the  autumn,  six  to  eight  inches  deep  and 
three  inches  apart,  and  remain  until  strong  groups  are  formed. 
These  groups  can  occupy  the  same  place  for  a  series  of  years, 
and  early  each  spring  the  flowers  begin  to  appear.  These 
narcissus  forms  are  also  especially  adapted  for  house  plants, 


FIG.  73.  —  A  daffodil. 


FLOWERS 


409 


three  or  more  bulbs  being  set  in  a  pot,  with  the  necks  of  the 
bulbs  at  the  surface  of  the  soil.  A  succession  of  plantings 
in  pots  will  yield  a  succession  of  flowers  throughout  the 
winter. 

117.  Tulip.  —  The  tulips  are  natives  of  the  oriental  coun- 
tries and  belong  to  the  lily  family  (Liliaceae).     The  origin 
of  the  common  garden  tulips  (Fig.  74)  is  unknown,  for  they 
had  been  long  under  cultivation  by  the  Turks  before  they 
came  under  the  observation  of  other  nations.     The  tulip 
has  a  curious  connection  with  the  history 

of  Holland,  for  its  introduction  into  that 
country  resulted  in  the  so-called  "  tulip- 
craze"  of  the  seventeenth  century,  a  craze 
which  compelled  the  interference  of  the 
government.  Holland  is  still  the  center 
of  the  development  of  tulip  bulbs. 

The  tulips,  like  the  daffodils  and  jon- 
quils, are  early  bloomers,  and  adapted  to 
cultivation  in  home  gardens.  The  bulbs 
are  set  out  in  the  autumn,  before  severe 
freezing,  in  sandy  loam  which  is  best  en- 
riched by  leaf -mould  and  well  drained.  The 
bulbs  are  planted  about  four  inches  deep 
and  four  to  five  inches  apart,  and  when  the  ground  begins  to 
freeze  the  bed  should  be  covered  with  leaves  or  other  light 
material.  In  the  spring,  when  severe  cold  is  over,  the  beds 
are  uncovered,  and  the  plants  will  probably  require  no  further 
attention.  In  the  selection  of  bulbs,  it  should  be  known  that 
the  size  of  the  bulb  is  not  so  important  as  an  abundance  of 
fibrous  roots. 

118.  Aster.  —  Asters  are  introduced  here  because  they 
are  late  bloomers,  and  belong  to  the  end  of  the  season,  as 
tulips,  daffodils,  and  jonquils  belong  to  the  beginning  of  the 
season.     Asters  belong  to  the  composite  family,  along  with 
the  chrysanthemum,  and  they  are  especially  abundant  as 


FIG.  74.  —  A  tulip. 


410 


ELEMENTARY   STUDIES   IN   BOTANY 


native  plants  in  North  America.  The  commonly  cultivated 
aster  (Fig.  75),  however,  is  not  an  aster,  but  is  a  near  relative, 
whose  fuller  name  is  "  China  aster."  As  the  name  suggests, 
it  is  a  native  of  China,  and  is  perhaps  the  favorite  fall- 
blooming  flower.  It  has  been  developed  into  "  double  " 
forms  of  various  kinds,  such  as  the  chrysanthemum,  and  its 
original  blue  has  been  extended  into  a  series  of  colors,  in- 
cluding red,  pink,  and  purple. 

The  seeds  are  sown  early  in  spring,  in  a  well-tilled  bed,  in 
shallow  rows  and  covered  with  fine  dirt.  When  the  plants 

appear,  they  are  thinned  out 
as  necessary,  and  the  soil  is 
cared  for  by  the  usual  tilling 
to  retain  moisture  in  dry 
weather.  A  bed  of  fall- 
blooming  asters  in  the  late 
autumn,  when  all  other  flow- 
ers are  gone,  well  repays  the 
little  care  it  involves. 

119.  Suggestions  for  work. 
-  The  very  few  flowers  de- 
scribed in  this  chapter  are 
intended  to  be  only  samples 
of  the  more  commonly  seen 
flowers,  and  the  list  should  be 
much  extended  by  observing  the  various  flowers  in  common 
cultivation  in  the  neighborhood,  both  in  home  gardens,  and 
by  florists.  A  visit  to  some  florist's  establishment  will  give 
some  idea  of  the  kinds  of  flowers  that  are  being  cultivated 
for  the  market  at  a  given  time. 

In  addition  to  these  observations  of  flowers  in  cultivation, 
some  of  the  more  rapidly  growing  forms  should  be  propa- 
gated as  a  part  of  the  laboratory  work,  and  other  represen- 
tative forms  should  be  brought  from  the  florist's  in  pots,  and 
not  only  observed,  but  also  cared  for. 


FIG.   75.  —  China  asters.  — •  After  BAILEY. 


CHAPTER  XI 


FIBER  PLANTS 

120.  General  statement.  —  While  fiber  plants  cannot  be 
included  among  those  of  common  cultivation,  they  cannot 
be  excluded  from  any  account  of  important  plants  culti- 
vated by  man.     Moreover,  some  of  them  are  of  such  great 
importance  that  every  student  of  plants  in  cultivation  should 
know  something  about  them.     There  are  hundreds  of  plants 
whose  fibers  might  be  used,  but  thirty  or  forty  species  at 
present  supply  the  plant  fibers  of  commerce. 

The  most  conspicuous  are  cotton  and  flax,  the  latter  being 
used  in  the  manufacture  of  linen.  After  these  come  the 
various  hemps  used  for  ropes, 
and  the  fibers  used  for  matting. 
A  brief  account  will  be  given  of 
the  origin  and  production  of 
these  most  important  fibers,  and 
it  will  be  easy  to  secure  speci- 
mens of  the  "  raw "  fibers, 
showing  how  they  appear  when 
connected  with  their  plants. 

121.  Cotton.  —  The    cotton 
plant  is  said  to  be  grown  over  a 
greater  area,  by  a  greater  num- 
ber of  people,  and  is  useful  for 
more  purposes  than  any  other 
fiber  plant.    Not  only  is  its  fiber 
exceedingly  important,  but  its 

seeds  yield  important  products,  among  which 
oil"  is  coming  to  be  generally  known. 

411 


FIG.    76.  —  Branch   of    cotton   plant, 
showing  foliage  and  flowers. — After 

W088IDLO. 


cotton-seed 


412 


ELEMENTARY    STUDIES   IN   BOTANY 


Cotton  is  a  member  of  the  mallow  family  (Malvaceae), 
which  is  characterized  chiefly  by  the  fact  that  its  numerous 
stamens  grow  together  to  form  a  tube  that  surrounds  the 

pistil  (Figs.  76  and  77). 
Associated  with  cotton 
in  this  family  are  such 
familiar  plants  as  holly- 
hock, the  mallows,  abuti- 
lon,  hibiscus,  etc.  The 
cotton  genus  (Gossypium) 
has  numerous  species, 
but  only  a  few  of  them 
are  cultivated  for  the 
fiber.  The  fiber  occurs 
on  the  seeds  in  a  fluffy,  woolly  mass  (Fig.  78),  and  the  seed- 
vessel  is  called  the  "boll"  (really  the  fruit  of  the  cotton 
plant).  It  is  easy  to  obtain  samples  of  these  bolls,  which 
burst  open  and  allow  the  mass  of  fibers  to  emerge  (Fig.  79). 


FIG.  77.  —  Section  of  a  cotton  flower,  showing  the 
large  petals  and  ^the  tube  formed  by  the  sta- 
mens. —  After  BAILLON. 


(l  \  IVv 

M  \vV& 


FIGS.  78  and  79.  —  Fiber  of  cotton :  fig.  78,  section  of  seed  with  fibers  attached  (after 
BAILLON)  ;  fig.  79,  a  cotton  boll,  burst  and  showing  the  mass  of  fibers  (after 
BAILEY). 

The  value  of  the  fiber  is  due  to  the  fact  that  it  has  a  twist 
that  makes  it  extremely  well  adapted  for  spinning. 

The  various  kinds   of  cotton  differ  in  the   quality  and 


FIBER   PLANTS  413 

length  of  the  fibers,  the  most  highly  prized  being  the  Sea 
Island  cotton,  with  its  long  and  silky  fibers.  This  cotton 
grows  to  the  greatest  perfection  along  the  coast  regions  of 
South  Carolina,  Georgia,  and  Florida.  There  is  also  "  up- 
land "  cotton  grown  in  the  United  States,  whose  fibers  are 
shorter  than  those  of  the  Sea  Island  cotton,  but  which  can 
be  cultivated  over  a  much  more  extensive  area  than  the 
finer  cotton.  In  the  market  the  various  cottons  are  graded 
according  to  the  length  of  the  fibers. 

It  is  well  known  to  every  school  boy  and  girl  that  a  new 
epoch  in  the  production  of  cotton  was  introduced  by  Whit- 
ney's invention  of  the  cotton  gin  in  1793 ;  and  from  that 
time  the  production  of  cotton  in  the  United  States  has  been 
an  increasing  industry  in  the  southern  states.  In  1860  the 
United  States  furnished  79  per  cent  of  the  cotton  used  in 
Europe,,  but  during  the  Civil  War  it  dropped  to  a  little  over 
3  per  cent;  in  1900  it  had  risen  again  to  80  per  cent.  In 
1911  the  total  cotton  production  of  the  United  States  was 
14,775,000  bales,  while  the  estimated  production  for  1912 
was  13,000,000  bales.  A  standard  bale  weighs  500  pounds. 

It  is  interesting  to  compare  the  production  of  cotton  in 
the  various  countries  of  the  world,  and  also  to  compare  its 
production  in  the  various  southern  states.  The  total  pro- 
duction of  cotton  in  the  world  cannot  be  known,  since  a  large 
amount  is  produced  and  used  in  countries  where  no  records 
are  kept.  The  following  figures,  therefore,  deal  only  with 
those  countries  from  which  information  can  be  obtained 
which  is  either  exact  or  approximate.  Taking  only  such 
countries  into  the  count,  the  world's  production  of  cotton 
in  1910  was  about  20,000,000  bales.  The  comparison  of 
cotton-producing  countries  in  1910  is  as  follows,  the  figures 
indicating  the  number  of  bales:  United  States  11,608,000, 
India  3,874,000,  Egypt  1,570,000,  China  1,200,000,  Russia 
688,000,  Brazil  270,000,  Mexico  200,000,  Turkey  141,000, 
Persia  128,000,  Peru  115,000. 


414  ELEMENTARY   STUDIES   IN   BOTANY 

In  comparing  the  production  of  cotton  by  states,  it  is 
interesting  to  note  the  changes  during  ten  years.  In  1900 
the  record  of  the  principal  cotton-growing  states,  in  the 
order  of  production,  the  numbers  indicating  bales  of  500 
pounds,  was  approximately  as  follows :  Texas  2,610,000, 
Mississippi  1,240,000,  Georgia  1,230,000,  Alabama 
1,000,000,  South  Carolina  840,000,  Arkansas  705,000, 
Louisiana  700,000,  North  Carolina  440,000,  Tennessee 


FIG.  80.  —  Map  shaded  to  show  the  states  of  greatest  cotton-production. 

210,000,  Indian  Territory  145,000,  Oklahoma  70,000, 
Florida  50,000;  all  other  states  nearly  30,000.  In  1911, 
when  the  total  production  was  approximately  15,000,000 
bales,  the  seven  principal  states  were  as  follows :  Texas 
4,200,000,  Georgia  2,770,000,  Alabama  1,700,000,  South 
Carolina  1,650,000,  Mississippi  1,200,000,  North  Carolina 
1,100,000,  Oklahoma  1,000,000,  all  other  states  about 
1,400,000  (Fig.  80). 

122.   Flax.  —  There  are  numerous  species  of  flax,  but  the 
common  form  in  cultivation  is  a  native  of  the  Mediterranean 


FIBER   PLANTS 


415 


region.  It  belongs  to  a  small  family  (Linacese),  which  re- 
ceived its  name  from  the' flax  genus  (Linum).  The  name  of 
the  common  flax  is  Linum  usitatissimum,  which  means 
"  most  useful  flax."  It  is  a  low  herb,  with  narrow  leaves 
and  handsome  blue  flowers  (Fig.  81). 

It  is  cultivated  for  the  fibers  of  its  stem  and  also  for  its 
seeds.  The  fibers  are  long,  fine,  and  very  strong,  so  that  it 
can  be  spun  into  very  stout  thread  (linen  thread)  and  woven 
into  very  durable  cloth  (linen) .  This 
fiber  is  also  used  when  especially 
strong  twine  or  rope  or  sails  are 
needed.  Every  one  is  familiar  with 
the  strong  body  of  oil-cloth,  which  is 
woven  of  flax  fiber.  The  seeds  yield 
the  well-known  linseed  oil,  used  for 
mixing  paints  and  varnishes,  and  in 
various  other  ways. 

This  very  useful  plant  has  been 
cultivated  from  the  earliest  times, 
but  now  its  most  extensive  cultiva- 
tion in  Europe  is  in  Russia,  Belgium, 
and  Ireland.  In  the  United  States 
it  has  been  cultivated  for  its  seed 
ever  since  the  first  settlements,  but 
lately  it  has  attracted  attention  as  a  fiber  plant,  especially 
in  Michigan,  Wisconsin,  Minnesota,  North  Dakota,  and 
Washington. 

The  world's  production  of  flaxseed  in  1898  was  about 
76,000,000  bushels,  Europe  producing  31,000,000  bushels, 
America  27,000,000  bushels,  and  India  18,000,000  bushels. 
In  the  same  year  the  production  of  fiber  was  about  1,800,000 
pounds,  all  of  which  is  credited  to  Europe.  About  ten  years 
later,  in  1909,  the  world's  production  of  flaxseed  amounted 
to  101,000,000  bushels;  and  in  1912  the  United  States  pro- 
duced about  28,000,000  bushels. 


FIG.  81.  —  A  flax  plant. 


416 


ELEMENTARY   STUDIES   IN   BOTANY 


Russia  leads  all  countries  in  the  production  of  both  seed 
and  fiber,  but  the  Belgian  flax  is  the  best,  clue  to  the  great 
care  taken  in  its  cultivation. .  Flax  demands  greater  labor 
than  almost  any  crop,  and  its  value  for  fiber  is  in  proportion 
to  the  amount  of  intelligent  care  it  receives.  For  fine  fiber 
the  seeds  are  sown  thickly,  so  that  the  plants  are  crowded, 
and  the  young  plants  are  pulled  before  the  seeds  are  mature. 
For  coarse  fiber,  the  plants  are  given  more  room  and  pulled 

when  the  seeds  are  nearly 
mature.  Usually  the 
plants  are  pulled  up  by 
hand,  roots  and  all,  and 
the  processes  used  for 
separating  the  fibers 
from  the  rest  of  the 
tissues  need  care  and 
labor.  Flax  is  said  to 
exhaust  the  soil  more 
than  any  other  crop, 
so  that  much  attention 
must  be  given  to  keep- 
ing the  soil  in  proper 
condition. 

123.  Hemp.  —  Fibers 
from  a  great  many  plants 
are  called  hemp,  but  the  common  hemp,  cultivated  from  the 
earliest  times,  belongs  to  the  nettle  family  (Urticacea).  Its 
name  is  Cannabis  sativa,  and  it  is  a  native  of  the  warmer  parts 
of  Asia,  but  it  has  become  naturalized  in  Europe  and  America. 
It  is  a  rough  herb,  with  palmately  compound  leaves  (Fig. 
82),  and  two  kinds  of  flowers  borne  on  different  plants 
(dioecious).  The  staminate  flowers  are  in  open  clusters, 
while  the  pistillate  flowers  are  in  compact  clusters  like  a 
spike.  The  hemp  plant  has  some  strange  associates  in  the 
nettle  family.  It  is  closely  allied  to  hops,  but  in  another 


FIG.    82.  —  A   hemp   plant.  —  After   Internat. 
Encycl. 


FIBER   PLANTS  417 

section  of  the  family  are  the  elms,  and  in  still  another  sec- 
tion are  the  figs,  mulberries,  and  nettles. 

Hemp  is  cultivated  for  its  fiber  in  all  the  countries  of 
Europe,  but  its  most  extensive  production  is  in  central  and 
southern  Russia,  which  supplies  the  largest  part  of  the 
world's  hemp.  In  the  United  States  it  is  cultivated  to  some 
extent,  especially  in  Kentucky,  Missouri,  and  Illinois ;  but 
its  production  in  this  country  has  been  greatly  reduced  by 
the  introduction  of  Manila  hemp. 

The  fiber  is  used  for  coarser  purposes  than  flax  fiber,  such 
as  for  ordinary  ropes,  for  calking  of  vessels,  etc.  The  seed 
is  also  produced  in  great  abundance  as  "  bird  seed  "  for  cage 
birds. 

The  name  "  hemp  "  has  been  applied  to  the  fibers  of  other 
plants  which  are  used  for  the  same  purposes,  the  most  con- 
spicuous of  which  are  "  bowstring  hemp,"  "  Manila  hemp," 
"  Sisal  hemp,"  and  "  Sunn  hemp."  These  will  serve  to 
illustrate  the  variety  of  plants  whose  fiber  can  be  used  in 
this  way. 

Bowstring  hemp  received  its  name  from  its  use  in  making 
bowstrings.  The  plant  belongs  to  the  lily  family  and  is 
native  in  the  tropical  jungles  of  both  eastern  and  western 
hemispheres. 

Manila  hemp  is  from  a  species  of  banana  growing  in  the 
Philippines,  where  it  is  extensively  cultivated.  It  is  a  very 
strong  fiber  and  has  come  to  be  used  in  the  United  States  for 
binding  twine  and  cordage. 

Sisal  hemp  is  from  an  agave  growing  in  Mexico,  Yucatan, 
and  the  West  Indies,  and  has  been  introduced  into  the 
Bahamas  and  Florida.  It  is  second  only  to  Manila  hemp  in 
strength. 

Sunn  hemp  is  from  a  member  of  the  legume  family  growing 
in  India.  It  is  not  as  strong  a  fiber  as  the  other  hemps 
mentioned  above,  but  it  makes  fairly  good  ropes,  canvas, 
etc. 


418  ELEMENTARY   STUDIES   IN   BOTANY 

124.  Suggestions  for  work.  —  Cotton  "  bolls  "  should  be 
obtained,  and  the  character  of  the  fibers  and  their  relation 
to  the  seeds  examined.  It  should  not  be  difficult,  also,  to 
obtain  samples  of  various  kinds  of  cotton  fiber,  "  staples," 
as  they  are  called.  Flaxseed  can  be  obtained  in  any  drug 
store,  and  young  flax  plants  can  be  grown  and  their  fibrous 
character  observed.  Wild  hemp  may  be  growing  in  the 
neighborhood  as  a  weed,  and  should  be  investigated. 


CHAPTER  XII 
FORESTRY 

125.  Definition.  —  Forestry  includes  so  many  things  that 
it  is  a  difficult  word  to  define.  Primarily  it  means  the  care 
of  forests,  but  it  has  often  come  to  include  also  the  care  of 
individual  trees.  Both  of  these  aspects  will  be  considered 
here. 

A  forest  is  often  called  "  woods  "  in  America,  and  the 
area  covered  varies  from  many  miles  in  extent  to  the  small 
"  wood-lots  "  that  remain  in  connection  with  many  home- 
steads. The  method  of  caring  is  the  same  whether  a  forest 
is  large  or  small.  The  abuse  of  forests  in  this  country  is 
well  known,  but  this  is  the  common  experience  of  new  coun- 
tries. The  time  has  now  come  when  we  have  begun  to 
realize  the  necessity  of  caring  for  our  forests,  and  among 
the  "  conservation  "  movements,  the  conservation  of  forests 
holds  a  very  important  place.  Forestry  is  an  application  of 
scientific  knowledge,  chiefly  botanical,  but  including  other 
sciences  as  well.  Some  indication  of  the  many  things  a 
forester  must  consider  will  help  to  an  understanding  of  his 
profession. 

Forestry  includes  not  only  such  detailed  care  of  forests  as 
will  be  indicated  later,  but  also  the  formation  of  forests 
where  they  do  not  exist,  either  because  they  have  been  re- 
moved ("  deforestation  ")  or  because  they  have  never  existed 
on  account  of  unfavorable  conditions.  The  forester  must 
keep  in  mind  always  the  purposes  of  a  forest  in  relation  to 
human  welfare,  which  are  principally  (1)  a  source  of  timber 
and  other  products,  and  (2)  to  check  floods  that  carry  off 
soil.  He  must  also  know  the  best  ways  of  using  forests, 

419 


420  ELEMENTARY    STUDIES   IN   BOTANY 

4 

and  this  includes  "  harvesting  the  crop/'  putting  it  into 
the  necessary  forms,  and  disposing  of  the  products.  The 
general  motive  of  forestry,  which  runs  through  all  of  its 
details,  is  to  use  the  forest  in  -such  a  way  that  it  may  not 
only  continue  to  be  productive,  but  increasingly  so.  To 
insure  this  will  require  adequate  protection  of  forest  property, 
a  more  complete  use  of  forest  products,  and  harvesting  with 
the  future  in  mind. 

126.  Character  of  the  forest.  —  An  assemblage  of  trees  is 
called  a  "  stand,"  and  stands  may  be  pure  or  mixed.  A 
pure  stand  is  one  in  which  all  the  trees,  or  nearly  all,  are  of 
the  same  kind ;  while  a  mixed  stand  is  one  in  which  there 
are  various  kinds  of  trees.  There  are  three  parts  of  a  forest 
to  consider  in  forestry :  (1)  the  canopy,  (2)  the  forest  floor, 
and  (3)  the  character  of  the  tree  trunks,  which  represent  the 
mass  of  wood. 

The  canopy  is  made  up  of  the  interlacing  crowns  of  the 
trees,  and  it  must  be  kept  as  uniform  as  possible.  The 
value  of  the  wood  depends  upon  this,  for  a  good  canopy 
causes  the  lower  branches  to  be  shed  while  they  are  small, 
and  as  a  result  the  trunk  is  clean  and  free  from  knots.  In 
the  formation  of  a  forest,  the  forester  sees  to  it  that  the 
canopy  rises  as  the  trees  grow.  In  a  pure  forest  a  uniform 
canopy  can  be  managed  easily,  but  in  a  mixed  forest  the 
canopy  is  a  more  complex  problem,  for  the  different  trees 
hold  different  relations  to  the  light,  some  needing  less  light 
than  others.  In  such  a  case  the  canopy  is  developed  in 
stories  in  accordance  with  the  light-needs  of  the  different 
trees.  The  canopy  serves  several  purposes  in  the  economy 
of  the  forest.  It  manufactures  the  carbohydrate  food  for 
the  trees ;  it  shades  the  forest  floor  and  thus  prevents  the 
development  of  undergrowth,  checks  the  drying  out  of  the 
soil,  and  shields  the  soil  from  dashing  rains ;  it  also  enriches 
the  soil  with  its  leaf  litter,  making  the  forest  soil  the  best  of 
soils. 


FORESTRY  421 

* 

The  forest  floor  is  not  merely  the  surface  of  the  soil,  but 
also  the  whole  soil  region  in  which  the  trees  are  rooted.  This 
is  usually  deep  and  rich,  but,  more  than  all,  the  humus  gives 
it  the  physical  properties  of  a  sponge  in  receiving  and  retain- 
ing water. 

The  character  of  the  tree  trunks  is  studied,  not  only  to 
insure  freedom  from  lower  limbs  by  means  of  a  suitable 
canopy,  but  also  for  the  development  of  wood.  Each  tree 
has  a  period  of  development  during  which  it  adds  annually 
to  its  wood  mass  enough  to  pay  for  the  room  and  care  it 
requires ;  but  eventually  it  reaches  a  stage  when  it  is  not  mak- 
ing enough  wood  "  to  pay  for  its  keep."  The  time  to  use  a 
tree,  therefore,  is  when  it  has  reached  its  maximum  wood- 
production  and  has  not  yet  begun  to  decline. 

127.  Forests  and  floods.  —  Forests  not  only  build  up  and 
enrich  the  soil,  but  they  also  fix  the  soil,  a  fact  of  great  im- 
portance especially  in  a  hilly  country.     The  interlacing  roots 
grasp  the  soil,  so  that  roots  and  soil  are  knit  together  in  a 
mass  that  resists  erosion.     It  can  be  observed  that  hillsides 
from  which  the  forest  has  been  removed  soon  become  gullied 
and  stripped  of  soil.     This  protection  against  erosion  serves 
not  only  for  the  soil  in  which  the  forest  grows,  but  also  for 
the  soil  of  the  fields  at  the  lower  levels. 

Forest  soil  holds  water  so  persistently  that  heavy  rains 
do  not  run  off  quickly  and  produce  floods,  as  they  do  in  bare 
regions.  It  is  often  remarked  that  streams  that  had  a 
steady  flow  when  a  region  was  first  settled  have  become 
alternately  flooded  and  dry  since  the  forests  were  removed. 
Therefore,  the  forest-covered  soil  not  only  prevents  erosion 
of  soil  and  flooded  streams,  but  provides  also  a  steady 
supply  of  water  to  the  streams. 

128.  Formation  of  forests.  —  It  would  not  be  useful  to 
give  the  details  involved  in  the  establishment  of  a  forest 
where  one  does  not  exist,  or  in  the  making  over  of  an  in- 
ferior forest,  but  some  idea  of  the  things  involved  will  add 

28 


422  ELEMENTARY    STUDIES   IN   BOTANY 

to  one's  information  as  to  the  work  of  a  forester.  Sometimes 
the  soil  must  be  reclaimed  by  draining  it  if  swampy,  and  by 
putting  it  into  better  physical  condition  if  necessary.  Great 
judgment  must  be  used  in  the  selection  of  trees  for  a  given 
region,  and  in  the  decision  whether  it  is  better  to  establish 
.a  pure  or  a  mixed  forest.  The  seed  used  must  be  tested 
thoroughly  for  quality,  and  the  care  of  seedlings  is  full  of 
details.  In  general,  the  germination  of  seeds  and  the  care 
of  seedlings  are  best  provided  for  in  reliable  nurseries.  In 
making  over  a  forest  of  inferior  quality,  the  problem  is  to 
give  seedlings  a  chance  to  grow  and  to  replace  the  old  and 
inferior  trees  by  young  and  vigorous  ones.  Of  course  each 
forest  has  its  own  problems,  but  enough  has  been  stated  to 
indicate  how  a  uniform  stand  may  be  secured  in  making  or 
reclaiming  a  forest. 

129.  Care  of  forests.  —  The  care  of  a  forest  means  keep- 
ing it  in  good  condition.  "  Cleaning  "  a  forest  means  the 
removal  of  useless  trees,  useless  because  they  are  dead  or 
injured  or  old  or  unpromising,  and  the  removal  of  other 
plants  and  of  brush  that  interfere  with  the  proper  condition 
of  the  forest  floor.  "  Thinning  "  a  forest  means  the  removal 
of  certain  trees  to  prevent  the  trees  from  interfering  with 
one  another.  This  interference  is  mostly  a  question  of  an 
over-crowded  canopy,  for  the  crowns  must  expand  freely 
and  interlace,  but  must  not  interfere  with  one  another's 
development.  Sometimes  pruning  is  helpful,  but  this  is 
not  practicable  in  a  large  forest  as  a  general  performance. 
The  advantage  of  forest  growth  in  the  production  of  wood 
as  contrasted  with  isolated  trees  should  be  understood.  A 
tree  "  in  the  open  "  is  often  thought  of  as  the  best  developed 
tree,  which  may  be  true  so  far  as  its  general  appearance  is 
concerned ;  it  satisfies  best  our  idea  of  how  a  tree  should 
look.  But  if  a  tree  is  expected  to  produce  wood  of  good 
quality,  it  must  be  associated  with  other  trees  so  that  a 
good  canopy  is  developed.  A  tree  in  the  open  produces 


FORESTRY  423 

more  wood,  but  it  is  poorer  in  quality  because  the  lower 
limbs  are  allowed  to  develop  and  the  wood  is  full  of  knots. 

130.  Protection  of  forests.  —  The  protection  of  forests  is 
one  of  the  most  difficult  problems  of  forestry,  for  it  involves 
the  passing  of  laws  and  their  enforcement,  and  the  hearty 
cooperation  of  communities.  This  is  especially  true  of  pro- 
tection against  fire,  which  is  the  greatest  enemy  of  the 
American  forest,  and  is  mostly  the  result  of  ignorance,  care- 
lessness, or  indifference.  The  fierce  fires  in  the  white  pine 
regions  of  Michigan,  Wisconsin,  and  Minnesota  have  become 
familiar,  and  sometimes  they  involve  extensive  destruction 
not  only  of  valuable  trees,  but  also  of  human  lives.  In  the 
great  Minnesota  fire  of  1904  it  is  reported  that  600  lives 
were  lost.  An  investigation  of  the  causes  of  these  recurring 
forest  fires  has  shown  that  sparks  from  passing  locomotives 
are  the  chief  cause.  It  is  evident  that  this  cause  of  fires 
can  be  controlled  if  public  sentiment  becomes  strong  enough. 
Another  prolific  cause  of  fires  comes  from  the  carelessness 
of  campers  and  hunters,  a  cause  that  is  troublesome  to  check. 
Farmers  often  "  clear  the  land  "  by  fire,  and  carelessness  or 
lack  of  judgment  may  result  in  permitting  the  fire  to  extend 
into  the  adjacent  forest.  The  effect  of  a  fire  differs  in  its 
destructiveness.  It  may  involve  only  the  canopy ;  it  may 
run  over  the  surface  of  the  soil ;  or  it  may  be  fierce  enough 
to  burn  the  humus  of  the  soil.  In  any  case,  the  forest  is 
crippled,  and  in  the  last  case  not  only  are  the  trees  destroyed, 
but  the  soil  is  no  longer  fit  for  forest  growth. 

The  danger  of  hard  freezing  is  also  to  be  considered,  for 
it  may  kill  the  buds,  crack  the  stems,  and  upheave  the 
young  plants.  Frost  cracks  in  lumber  show  that  damage 
from  this  cause  is  often  serious.  The  trees  cannot  be  pro- 
tected from  such  a  danger  completely,  but  a  dense  canopy 
reduces  it,  and  a  thick  litter  of  decaying  leaves  (humus)  on 
the  forest  floor  is  still  further  protection.  Damage  is  also 
done  by  violent  winds,  hail  storms,  sleet,  and  snow,  but 


424  ELEMENTARY   STUDIES   IN   BOTANY 

these  are  the  accidents  of  nature  that  involve  only  a  repair 
of  the  damage. 

There  are  many  insects  which  are  very  destructive  to  trees 
because  they  bore  into  «the  wood  or  eat  the  leaves.  The 
gipsy  moth  has  become  famous  for  its  leaf -destroying  powers. 
The  best  protection  against  insects  is  to  encourage  their 
enemies.  A  forest  full  of  birds,  toads,  snakes,  etc.,  is  well- 
protected  against  destructive  insects.  The  need  for  such 
protection  justifies  the  exclusion  of  hunters  from  forests  under 
cultivation,  especially  the  men  who  shoot  at  everything. 

The  problem  of  grazing  animals  in  a  forest  is  a  mixed  one. 
These  animals  are  usually  sheep,  and  up  to  a  certain  num- 
ber they  may  not  be  injurious,  and  may  even  be  helpful, 
but  in  large  numbers  they  are  injurious,  being  not  only 
grazing  but  also  browsing  animals. 

The  danger  to  forests  from  plant  diseases  will  be  con- 
sidered in  the  next  chapter,  which  deals  with  plant  diseases 
in  general. 

131.  Forest  products.  —  It  is  a  surprise  to  many  to  dis- 
cover the  number  of  uses  to  which  forest  trees  are  put. 
Most  people  probably  think  of  forests  only  as  a  source  of 
lumber,  so  far  as  their  commercial  use  is  concerned.  It  is 
true  that  lumber  is  the  conspicuous  product,  arid  it  is  known 
that  this  lumber  is  put  to  endless  uses.  For  this  purpose, 
trees  are  grouped  as  "  soft  woods  "  (pine,  spruce,  hemlock, 
cedar,  etc.),  belonging  to  the  conifer  group  (called  "  ever- 
greens "  by  many),  and  "  hard  woods  "  (oak,  walnut,  hickory, 
cherry,  locust,  tulip-tree,  ash,  maple,  elm,  cottonwood,  etc.). 
The  lumber  industry  in  soft  woods  may  be  used  as  an  illus- 
tration. The  most  prized  soft  wood  is  the  white  pine,  and 
the  important  white  pine  states  are  Michigan,  Wisconsin, 
and  Minnesota.  This  valuable  tree  has  been  harvested  so 
recklessly  that  it  has  now  approached  dangerously  near  the 
point  of  extinction  as  a  commercial  source  of  lumber.  The 
lumber  camps,  logging  operations,  and  the  floating  out  of 


FORESTRY  425 

the  lumber  are  important  features  of  these  states,  and  have 
developed  a  type  of  life  and  a  race  of  hardy  men  (chiefly 
French  Canadians)  who  have  appeared  in  many  stories. 
In  the  south  the  yellow  pine  is  the  great  soft  wood.  As  it 
grows  in  an  open,  level  forest,  the  logging  operations  differ 
from  those  of  white  pine,  and  are  by  no  means  so  picturesque. 
The  logs  are  simply  hauled  to  the  railway  or  mill,  and  the 
work  is  done  chiefly  by  negroes.  The  third  great  region  for 
soft  wood  lumber  is  in  the  northwest,  in  the  Douglas  spruce 
and  redwood  forests  of  the  Pacific  slope,  where  the  immense 
size  of  the  trees  and  the  roughness  of  the  ground  have  neces- 
sitated special  methods  and  machinery  entirely  unknown  in 
other  regions. 

The  use  of  wood  pulp  in  the  manufacture  of  paper  is  a 
tremendous  industry.  The  most  commonly  used  wood  is 
spruce,  and  the  process  consists  in  grinding  the  wood  (from 
which  bark  and  knots  are  removed)  into  pulp  and  pressing 
it  into  paper.  This  pressed  pulp,  aside  from  paper  manu- 
facture, is  used  in  the  manufacture  of  a  great  variety  of 
articles,  as  buckets,  doors,  and  even  wheels.  In  the  manu- 
facture of  paper  it  is  estimated  that  one  ton  of  paper  pulp 
is  produced  by  one  and  a  half  cords  of  wood.  The  amount 
of  this  paper  used  by  newspapers  is  enormous.  It  has  been 
estimated  that  one  large  newspaper  uses  in  one  year  all  the 
spruce  grown  on  16,000  acres  of  land,  as  spruce  naturally 
grows.  If  this  amount  be  multiplied  so  as  to  include  all  the 
newspapers,  it  is  evident  that  the  supply  of  spruce  will  fail. 
Of  course  other  woods  can  be  used  for  the  same  purpose, 
Carolina  poplar  making  very  good  paper  pulp. 

The  pines  are  used  as  the  source  of  resin  and  turpentine, 
which  occur  in  "  crude  resin  "  in  the  resin  ducts  of  the  wood. 
The  largest  supply  of  this  product  comes  from  the  pine 
forests  of  the  south,  but  in  collecting  it  the  trees  are  so  handled 
that  they  are  destroyed.  In  France  the  product  is  obtained 
without  destroying  the  trees,  and  unless  some  such  method 


426  ELEMENTARY    STUDIES   IN   BOTANY 

is  introduced  in  the  southern  pineries,  the  resin  industry  is 
doomed  to  destruction. 

The  bark  of  certain  trees  is  also  used  as  a  source  of  tannic 
acid  for  tanning  leather.  In  Europe,  oaks  are  extensively 
propagated  for  this  purpose,  but  in  the  United  States  hem- 
lock bark  is  used.  With  our  usual  recklessness  the  trees 
are  practically  destroyed  in  securing  the  bark,  so  that  now  a 
large  amount  of  our  tannin  comes  from  South  American 
woods. 

The  destructive  distillation  of  woods  yields  a  remarkable 
variety  of  products  that  need  not  be  enumerated,  chief 
among  which  are  wood  alcohol  and  tar  (from  the  distillation 
of  pine).  In  every  case,  after  the  desired  product  has  been 
driven  off  by  distillation,  charcoal  is  left. 

Any  consideration  of  the  products  of  trees  must  include 
maple  sugar  and  syrup.  This  is  said  to  be  the  only  forest 
industry  that  has  been  developed  on  a  scientific  basis.  It  is 
an  American  industry,  and  when  it  is  known  that  over 
50,000,000  pounds  of  sugar  and  3,000,000  gallons  of  syrup 
are  produced  each  year,  it  can  be  appreciated  that  the  indus- 
try is  a  large  one.  Vermont  is  the  leading  state  in  maple 
sugar  production,  producing  15,000,000  pounds  of  sugar  and 
100,000  gallons  of  syrup  in  a  year. 

In  this  connection  mention  may  be  made  of  the  common 
sources  of  commercial  sugar.  Sugar-cane  (a  grass)  has 
been  used  longest  as  a  source  of  sugar,  and  in  this  country 
the  industry  has  been  most  developed  in  Louisiana.  The 
manufacture  of  sugar  from  beets  is  a  much  newer  industry, 
and  has  developed  on  a  large  scale  in  the  United  States.  In 
the  production  of  sugar  from  sugar-cane,  India  leads  the 
other  countries,  followed  by  Cuba,  Java,  and  the  United 
States.  The  world's  production  of  sugar  from  cane  in  1903 
is  estimated  to  have  been  about  4,000,000  tons ;  and  of  sugar 
from  beets  about  5,800,000  tons,  5,600,000  tons  of  which  was 
produced  in  Europe.  In  1911  the  production  of  sugar  from 


FORESTRY  427 

cane  had  reached  7,600,000  tons,  and  from  beets  8,400,000 
tons. 

Another  use  of  forest  products  has  yet  to  be  developed  in 
the  United  States.  In  Europe  every  twig  is  used ;  that  isr 
the  forest  refuse,  which  we  destroy  as  "  brush,"  is  all  utilized. 
To  use  this  material  seems  to  the  American  a  waste  of  time, 
involving  an  amount  of  labor  that  is  not  paid  for  by  the 
result;  but  since  many  uses  for  forest  refuse  have  been 
developed  in  European  countries,  there  is  no  reason  why 
some  of  them  may  not  be  introduced  here. 

132.  Forest  reservations.  —  The  great  importance  of 
exercising  some  control  over  forests  has  led  the  national 
government  to  adopt  a  system  of  forest  reservations,  which 
are  under  its  care.  To  a  certain  extent,  states  have  done 
the  same  thing,  but  it  will  be  impossible  to  include  them  in 
this  brief  statement.  It  is  not  the  purpose  of  the  govern- 
ment to  withdraw  such  forests  from  use,  but  rather  to  super- 
vise their  use  so  that  they  may  continue  to  be  productive. 
Furthermore,  some  forests  are  reserved  by  the  government 
not  so  much  for  the  sake  of  a  continuous  timber  supply,  as 
to  protect  certain  regions  from  floods  and  soil  destruction. 
Naturally  such  forests  are  found  on  the  important  water- 
sheds of  our  drainage  systems. 

These  reservations  are  so  fluctuating  in  extent,  depending 
upon  the  attitude  of  the  president  towards  forest  reservation, 
that  it  is  impossible  to  give  their  exact  extent  as  a  general 
statement.  Some  conception  of  the  forest  areas  involved, 
however,  and  their  distribution  may  be  obtained  from  the 
following  statement  of  the  reservations  in  1901,  the  begin- 
ning of  such  reservations  being  in  1891.  The  statement, 
therefore,  covers  the  period  of  the  first  ten  years  of  forest 
reservation.  During  that  period  nearly  50,000,000  acres 
of  forest  land  were  reserved,  distributed  among  13  states. 
The  list  of  states,  the  number  of  reservations,  and  the 
approximate  number  of  acres  involved  are  as  follows,  in 


428  ELEMENTARY   STUDIES   IN   BOTANY 

the  order  of  total  size  of  area  in  each  state :  California,  nine 
reservations,  8,750,000  acres ;  '  Washington,  three  reserva- 
tions, 7,000,000  acres ;  Arizona,  four  reservations,  5,000,000 
acres ;  Oregon,  three  reservations,  4,750,000  acres  ;  Montana, 
three  reservations,  4,500,000  acres ;  Idaho  and  Montana, 
one  reservation  in  common,  4,000,000  acres ;  Wyoming,  four 
reservations,  3,250,000  acres ;  Colorado,  five  reservations, 
3,000,000  acres;  New  Mexico,  two  reservations,  2,750,000 
acres ;  South  Dakota  and  Wyoming,  Black  Hills  reserva- 
tion, 1,200,000  acres;  Utah,  three  reservations,  1,000,000 
acres ;  Idaho  and  Washington,  one  reservation  in  common, 
650,000  acres ;  Alaska,  one  reservation,  400,000  acres  ; 
Oklahoma,  one  reservation,  60,000  acres.  This  list  includes 
41  reservations  set  apart  as  forests ;  but  since  1901  the 
amount  of  reservation  has  been  very  much  increased,  the 
total  area  in  1912  approximating  190,000,000  acres.  An 
illustration  of  the  increase  can  be  obtained  from  Alaska, 
whose  area  of  reservation  increased  from  400,000  acres  in 
1901  to  27,000,000  acres  in  1912. 

133.  Street  trees.  —  Even  though  the  reader  of  this  book 
may  not  have  access  to  a  forest,  where  forest  conditions  can 
be  observed,  he  can  at  least  observe  trees  growing  in  yards 
or  along  streets.  In  fact,  the  study  of  trees,  even  in  cities, 
is  not  only  possible,  but  interesting  and  profitable.  There  is 
nothing  more  neglected  than  street  trees,  and  it  will  be  helpful 
if  school  pupils  are  taught  to  know  something  about  their  care. 

The  streets  fitted  for  tree-planting  usually  provide  a 
planting  strip  between  the  sidewalk  and  the  curb ;  and  in  a 
very  wide  street  a  parking  strip  in  the  middle  is  often  seen. 
Much  street  planting  has  been  done  independently  by  the 
owners  of  different  lots,  so  that  the  trees  are  of  various  kinds 
and  the  result  is  a  ragged  appearance.  If  possible,  a  reason- 
able uniformity  in  the  kind  of  tree  used  improves  the  ap- 
pearance of  a  street  very  much.  Not  only  should  the  trees 
be  of  the  same  kind,  but  their  spacing  should  be  uniform, 


FORESTRY  429 

and  this  differs  for  different  trees.  The  spacing  should  be  a 
little  greater  than  the  natural  spread  of  a  tree ;  for  example, 
the  following  spacings  are  recommended :  white  elm,  50 
feet ;  maples,  40-45  feet  (dependent  on  the  kind) ;  linden, 
40  feet ;  Carolina  poplar,  30  feet. 

The  selection  of  trees  is  important,  and  the  judgment  of 
different  people  will  vary.  The  primary  choice  is  between 
a  fast-growing  tree  and  a  slow-growing  tree.  The  former 
brings  results  quicker,  which  mean  beauty  and  shade,  but 
it  is  usually  a  short-lived  and  brittle  tree.  The  latter  de- 
velops beauty  and  shade  very  slowly,  but  it  is  usually  long- 
lived  and  tougher.  It  would  seem  wise  to  select  for  city 
streets  the  slow-growing  and  long-lived  trees,  the  most  popu- 
lar of  which  is  the  white  or  American  elm.  The  rapid-grow- 
ing trees,  which  impatient  people  select,  are  usually  Carolina 
poplar,  willow,  box  elder,  or  silver  maple. 

134.  Planting  street  trees.  —  The  space  for  soil  prepara- 
tion is  very  restricted,  so  that  instead  of  breaking  up  the 
soil  in  the  usual  way  for  a  crop,  large  holes  are  dug  and 
filled  with  proper  soil,  which  in  this  case  means  a  pulverized 
soil  thoroughly  mixed  with  fine  manure.  Great  care  must 
be  taken  to  see  that  there  is  proper  drainage,  and  often  a  tile 
drain  has  to  be  laid.  The  young  trees  are  usually  obtained 
from  a  nursery,  and  before  they  are  "  set,"  they  are  pruned, 
so  that  the  stem  system  may  balance  better  the  more  or 
less  injured  root  system.  In  case  the  root  system  is  com- 
plete, no  trimming  is  necessary,  but  it  would  be  a  rare 
amount  of  care  that  could  transplant  a  young  tree  without 
injuring  the  roots  more  or  less.  In  the  bottom  of  the  hole 
a  bed  of  fine  soil  is  placed,  the  tree  is  settled  in  place  care- 
fully and  watered,  and  the  hole  filled  up.  Of  course  trees 
must  be  transplanted  while  they  are  dormant,  and  this 
means  either  spring-planting  or  fall-planting,  the  former 
being  the  better.  Sometimes  very  large  trees  are  trans- 
planted, but  the  larger  the  tree,  the  greater  the  danger. 


430  ELEMENTARY   STUDIES   IN   BOTANY 

135.  Care   of   street   trees.  —  In   observing   most   street 
trees,  one  might  infer  that  after  the  trees  are  planted  they 
need  no  attention.     While  they  need  little  attention  after 
they  are  full  grown,  the  young  and  growing  trees  cannot  be 
neglected.     Perhaps   the   greatest   cause   of   failure   in   the 
growing  of  street  trees  is  the  poor  physical  condition  of  the 
soil,  a  thing  which  the  reader  of  this  book  might  infer.     The 
soil,  therefore,  must  be  kept  in  good  physical  condition  around 
the  young  trees,  and  since  the  feeding  ground  of  street  trees 
is  much  restricted,  certain  fertilizers  are  a  great  help.     It  is 
evident  that  the  cultivation  of  the  soil  beneath  the  tree 
helps  the  movement  of  air  through  the  soil  and  helps  the 
soil  retain  moisture.     If  there  is  sod  around  a  tree,  it  should 
be  broken  up  every  few  years. 

Of  course  street  trees  must  be  pruned,  and  pruning  is 
done  while  the  tree  is  dormant.  In  connection  with  pruning, 
the  large  wounds  (over  two  inches  in  diameter)  must  be 
cared  for,  or  they  will  permit  the  entrance  of  destructive 
fungi.  They  are  dressed  with  something  that  excludes 
fungi,  as  thick  paint  or  coal  tar.  When  a  wound  is  very 
large  (over  six  inches  in  diameter),  it  is  usually  covered  after 
treatment  with  a  zinc  plate,  a  process  called  "  tinning." 
Wounds  less  than  two  inches  in  diameter  usually  heal  up 
before  the  fungi  effect  an  entrance. 

136.  Injuries  to  city  trees.  —  There  are  many  sources  of 
injury  to  city  trees,  due  chiefly  to  city  conditions.     Smoke 
poured  out  abundantly  from  smoke  stacks,   and  gas  from 
leaking  pipes  escaping  into  the  soil   about  the  roots,   are 
common  causes  of  dead  and  dying  trees  seen  along  streets. 
Electric  linemen  are  often  reckless  in  chopping  out  branches 
to  clear  the  way  for  wires.     Trees  are  also  often  seen  to  be 
used  for  anchoring  guy  ropes.     Regrading  streets  often  de- 
stroys  trees   ruthlessly   and   needlessly.     Ignorant   pruning 
probably  destroys  more  trees  than  any  other  danger,  not 
only  because  the  pruning  is  wrong,  but  also  because  the 


FORESTRY  431 

wounds  are  not  cared  for.  The  old  days  of  using  trees  for 
hitching  posts  and  subjecting  them  to  wounding  by  horse 
bites  have  nearly  passed.  Of  course  storms  are  to  be  reckoned 
with,  and  a  sheeting  of  ice  breaks  many  twigs  and  even  large 
limbs.  The  best  protection  against  damage  from  such  storms 
is  to  select  for  street  trees  those  that  are  not  brittle.  The 
Carolina  poplar,  willow,  and  silver  maple  are  notably  brittle, 
and  after  a  storm  the  ground  beneath  them  is  strewn  with  a 
litter  of  branches. 

137.  Suggestions  for  work.  —  If  a  forest  is  available,  it 
should  be  visited  by  all  means.  The  trees  should  be  named, 
the  crown  examined,  the  uniformity  or  irregularity  of  growth 
noted,  and  judgment  passed  as  to  the  condition  of  the  forest 
and  its  needs. 

Special  pains  should  be  taken  to  learn  to  recognize  all  the 
common  street  and  yard  trees  in  the  vicinity,  both  in  their 
winter  condition  (from  their  habit  and  bark)  and  foliage 
condition.  Street  trees  should  be  examined  to  discover 
their  condition  and  the  care  they  are  receiving ;  if  any  work 
is  being  done  with  them,  it  should  be  watched.  If  trees  are 
sickly  looking,  the  cause  should  be  inquired  into.  This 
kind  of  interest  in  street  trees  will  stimulate  the  community 
to  a  more  intelligent  care  of  them. 


CHAPTER  XIII 
PLANT  DISEASES 

138.  Definition.  —  In  the  cultivation  of  plants  there  must 
be  some  knowledge  of  the  diseases  to  which  they  are  subject. 
Sometimes  whole  crops  are  destroyed  by  some  disease,  or 
at  least  much  reduced  in  quantity  and  quality.  The  great 
losses  from  this  cause  have  led  the  national  and  state  gov- 
ernments to  provide  for  the  study  of  plant  diseases  in  the 
hope  of  preventing  them.  Very  much  has  been  accom- 
plished, but  very  much  more  remains  to  be  done.  A  multi- 
tude of  facts  in  reference  to  diseases  and  treatments  have 
been  accumulated,  but  these  cannot  be  detailed  here.  Only 
the  general  facts  in  reference  to  plant  diseases  and  the  general 
principles  of  treatment  can  be  indicated ;  for  special  details 
the  student  must  consult  the  larger  works  in  which  the 
known  facts  are  assembled. 

It  is  difficult  to  define  exactly  what  is  meant  by  a  plant 
"  disease."  In  a  large  sense  it  is  anything  that  interferes 
with  the  normal  activities  of  a  plant,  so  that  it  is  not  "  doing 
well."  It  is  evident  that  this  would  include  a  great  variety 
of  causes,  such  as  soil  conditions,  climatic  conditions,  me- 
chanical injuries,  attacks  of  animals  (especially  insects),  and 
attacks  of  parasitic  fungi ;  in  fact,  anj^thing  that  affects 
unfavorably  the  vigor  of  a  plant.  It  is  clear  that  we  can 
include  no  such  indefinite  range  of  causes,  and  must  restrict 
ourselves  to  the  diseases  induced  by  parasitic  fungi,  for 
these  are  the  most  common  and  most  studied  of  the  diseases. 

The  distinction  between  a  disease  and  its  cause  must  be 
kept  clear.  A  parasite  (like  wheat  rust,  for  example)  is  a 
cause,  but  the  disease  is  the  condition  of  the  attacked  plant 

432 


PLANT   DISEASES  433 

(host)  brought  about  by  the  presence  of  the  parasite,  a  con- 
dition which  is  more  or  less  unfavorable  to  the  work  of  the 
plant.  This  means  that  while  we  investigate  the  parasite 
to  discover  its  habits,  the  patient  that  has  the  disease  is  the 
host  plant.  The  study  of  plant  diseases,  therefore,  so  far  as 
plant  parasites  are  concerned,  is  the  study  of  the  effect  of 
the  parasite  on  the  host  plant. 

The  practical  application  of  our  knowledge  of  parasites 
and  diseases  has  not  resulted  so  much  in  curing  diseases  as 
in  preventing  them,  which  means  preventing  the  attack  of 
parasites.  This  involves  enough  knowledge  of  the  parasite 
to  know  the  form  in  which  it  makes  its  attack,  as  well  as  the 
part  attacked  and  the  time  of  attack. 

139.  The  groups  of  parasites.  —  Almost  all  of  the  groups 
of  fungi  contain  parasites  that  are  dangerous  to  cultivated 
plants.     These  parasites  are  more  or  less  selective,  that  is, 
they  do  not  all  attack  all  plants  indiscriminately.     Each 
parasite  is  more  or  less  restricted  to  certain  hosts,  and  often 
to  a  single  host.     This  explains  why  one  kind  of  plant  is 
subject  to  a  certain  disease  ("  susceptible  "),  and  another 
is  not  ("  immune  "). 

The  groups  of  parasites  are  very  numerous,  and  it  would 
be  impossible  for  an  elementary  student  to  learn  to  recog- 
nize them ;  but  this  is  not  important  for  our  purpose.  All 
that  is  necessary  in  this  first  contact  is  to  learn  to  recognize 
certain  "  symptoms "  of  disease  which  attacked  plants 
show.  Any  symptom  suggests  troubles  which  may  be 
brought  about  by  a  great  variety  of  parasites,  and  it  is  not 
always  necessary  to  distinguish  the  -parasite  exactly  before 
using  the  appropriate  preventive  measures. 

140.  The  groups  of  diseases.  —  All  plant  diseases  can  be 
referred  to  three  groups,  which  differ  as  to  the  relation  of 
parasite  and  host. 

In  one  group,  the  parasite  kills  living  cells,  and  its  de- 
structiveness  depends  upon  the  number  and  kind  of  cells 


434 


ELEMENTARY    STUDIES   IN   BOTANY 


killed.  A  plant  attacked  by  such  a  parasite  may  live  along 
in  a  more  or  less  enfeebled  way,  or  it  may  be  destroyed 
completely. 

In  a  second  group,  the  parasite  does  not  kill  living  cells, 
but  lives  in  association  with  them,  feeding  upon  their  prod- 


FIG.   83.  — A  spot  disease  of  apple  leaf.  —  After  SORAUER. 

ucts.  Often  as  a  result  of  the  presence  of  such  a  parasite, 
the  living  cells  are  "  stimulated  "  into  doing  unusual  things, 
such  as  the  development  of  "  galls  "  or  other  unusual  growths. 
Such  growths  are  symptoms  of  the  presence  of  such  a  para- 
site. This  peaceful  living  together  is  usually  brought  to  an 
end  when  the  parasite  begins  to  form  spores. 


PLANT   DISEASES  435 

In  a  third  group  the  parasites  neither  destroy  living  cells 
nor  live  peaceably  with  them,  but  invade  the  water-conduct- 
ing vessels  (woody  fibres)  and  live  in  the  sap.  This  inter- 
feres with  the  movement  of  water,  and  if  the  parasites 
develop  so  as  to  block  the  vessels,  the  water  supply  is  cut 
off  and  the  plant  wilts.  These  "  wilt  diseases  "  are  very 
common  and  destructive,  especially  in  the  case  of  seedlings. 


Fiu.  84. — A  spot  disease  of  maple  leaf.  —  After  SORAUER. 

141.  Diseases  of  the  first  group.  —  In  this  group  of  dis- 
eases the  parasite  kills  living  cells.  No  list  of  these  diseases 
can  be  given,  but  a  few  representative  cases  will  illustrate 
them. 

Pear  blight.  —  This  is  one  of  the  common  diseases,  not 
only  of  pear  trees,  but  of  apple  trees  and  other  fruit  trees. 
It  is  sometimes  called  "  fire  blight  "  or  "  twig  blight,"  and 
these  names  suggest  the  appearance  of  trees  with  this  dis- 
ease. The  flowers  and  branch  tips  begin  to  wilt  and  finally 
blacken,  and  this  may  extend  to  every  branch  tip,  until  the 


436 


ELEMENTARY    STUDIES   IN   BOTANY 


tree  appears  as  though  its  branches  had  been  badly  scorched 
with  fire.  This  disease  is  caused  by  certain  bacteria  that 
spread  through  the  living  cells' and  destroy  them.  It  is 
always  necessary  to  determine  how  a  parasite  effects  an 
entrance  in  a  plant,  for  this  suggests  the  method  of  preven- 
tion. The  entrance  of  a  parasite  is  spoken  of  as  an  "  infec- 


FIG.   85.  —  A  spot  disease  of  currant  leaf.  —  After  HALL. 

tion,"  and  in  the  case  of  pear  blight,  it  is  found  that  the 
infection  is  brought  about  by  insects  (especially  bees)  visit- 
ing the  flowers.  This  infection  spreads  to  other  flowers  and 
through  them  into  the  young  twigs.  Just  how  the  insects 
get  the  bacteria  is  a  detail  that  is  not  needed  for  practical 
purposes. 

Spot    diseases.  —  It  is  very  common  to  see  leaves  spotted, 


PLANT   DISEASES 


437 


the  spots  indicating  that  they  have  been  attacked  by  some 
fungus  (Figs.  83-87).  Among  the  parasites  that  produce 
spotted  leaves  are  the  "  mildews."  One  kind  of  mildew  is 
called  the  "  downy  mildew"  because  it  appears  on  the  sur- 
face (usually  leaf)  of  the  host  plant  as  small  downy  patches. 


FIG.  86.  —  A  spot  disease  of  strawberry 
leaves. — After  MASSEE. 


These  patches  are  numerous  minute  branches  bearing  spores, 
that  have  arisen  from  the  parasite  deep  within  the  host, 
where  it  is  destroying  living  cells.  Before  the  downy  patches 
appear,  the  presence  of  such  a  parasite  in  a  leaf  is  shown 
by  the  dying  and  dead  spots.  This  attack  on  leaves  reduces 
their  ability  to  manufacture  food,  and  it  may  be  so  general 

an   attack  that   the   leaves   are   destroyed   entirely.     Such 
29 


438 


ELEMENTARY    STUDIES   IN   BOTANY 


attacks  are  common  on  many  vegetables,  as  radishes,  tur- 
nips, cucumbers,  onions,  lettuce,  etc.,  but  the  most  con- 
spicuous case  is 
that  of  the  grape 
(Fig.  88). 

These  mildews 
represent   one  of 
the  most  destruc- 
tive of  the  "dis- 
of     the 


eases 
grape-vine, 


the 


FIG.   87.  — A  spot  disease  of  beet  leaf.  —  After  HALSTED. 


most  susceptible 
grape  being  the 
wine  grape  ( Vitis 
vinifera)  of  Eu- 
rope and  Cali- 
fornia. In  the 
account  of  the 
grape  (p.  396)  it 
was  stated  that 
the  wine  grape 
could  not  be 
grown  in  our 
eastern  states  on 
account  of  this 
disease.  It  can 
be  grown  in  Eu- 
rope and  Califor- 
nia because  for 
some  reason  the 
destructive  mil- 


dew is  absent  or  is  harmless.  Infection  in  this  case  is  by 
spores  that  fall  upon  young  leaves,  and  the  suggested  pre- 
vention is  to  destroy  the  spores  in  some  way  before  they  can 
effect  an  entrance. 


PLANT   DISEASES 


439 


Another  kind  of  mildew  ("  powdery  mildew  ")  attacks  the 
young  grapes,  producing  corky  spots  that  destroy  the  value 


FIG.  88. — Grape  leaf,  showing  patches  of  downy  mildew. 

of  the  fruit.  This  spotting  of  the  fruit  does  not  destroy  the 
plant,  for  it  is  only  a  skin  disease,  but  it  destroys  the  value 
of  the  plant  for  our  use. 


440 


ELEMENTARY    STUDIES   IN   BOTANY 


Potato  disease.  —  This  is  a  notable  and  dangerous  disease. 
Famines  in  Ireland  have  been  brought  about  by  its  ravages, 
because  in  destroying  the  potato  crop  there  were  no  other 
crops  to  replace  it  as  a  food  supply.  The  spores  of  the 

parasite  enter  the 
young  leaves  and 
they  begin  to  spot 
(Fig.  89),  and  fi- 
nally the  parasite 
invades  all  the 
leaves  and  the 
young  stem,  and 
the  plant  dies. 
The  disease  is 
so  very  epidemic 
that  if  it  enters 
^v-.-£,-  ••-*>*  a  potato  field,  it 

^fH  Ifc  B  f^  life.         sweeps  through  it 

H  W*     w^  great  rapid- 

^^^SBB  mr      '      ity.    If  the  attack 

is  early  in  the  sea- 

fj^i5^  son,  the  formation 

%  of  tubers  may  be 

^j|  .        stopped;    if  it  is 

later,  the  tubers 
may  have  begun 
to  develop,  and 
in  this  case  the 
tubers  also  are  in- 
vaded. Tubers  in  this  condition  are  said  to  have  the 
"  potato  rot"  (Fig.  90),  but  the  rotting  is  not  caused  by 
the  destructive  parasite ;  it  is  merely  the  natural  rotting  of  a 
plant  structure  that  has  been  killed.  This  is  one  of  the 
hardest  diseases  to  prevent,  for  since  potatoes  are  propa- 
gated by  tubers,  the  danger  of  infected  tubers  is  very  great. 


FIG.  89. —  Potato  disease  on  the  leaves.  — After  JONES. 


PLANT   DISEASES 


441 


Stone  fruit  diseases.  —  The  common  disease  of  stone  fruits 
is  the  "  brown  rot,"  and  probably  its  destructiveness  is 
noticed  more  in  the  case  of  peaches  than  in  any  other  one 
of  the  stone  fruits  (plum  and  cherry),  many  of  the  "  failures  " 
of  the  peach  crop  being  due  to  it.  Along  with  the  peach 


FIG.  90.  —  Potato  disease  ("potato  rot  ")  in  tubers. — After  DUGQAK. 

are  associated  its  near  relatives,  the  apricot  and  the  nec- 
tarine. In  this  case  the  fruit  is  infected  directly  by  the 
spores  of  the  parasite,  and  it  seems  to  be  most  susceptible 
from  the  time  it  is  half  grown  until  it  ripens.  The  first 
symptom  of  the  attack  is  a  small,  brown,  decayed  spot  which 
increases  in  size  until  the  whole  fruit  is  infected.  Often  the 


442 


ELEMENTARY    STUDIES   IN   BOTANY 


fruit  is  completely  dried  out,  and  such  "  mummies/'  as  they 
are  called,  may  be  seen  hanging  on  the  trees.  It  should  be 
realized  that  these  mummies  are  exceedingly  dangerous,  for 
they  are  the  chief  source  of  infection  the  next  year.  Often 

infections  are  so  late 
that  the  disease  is  not 
detected  until  after  the 
fruit  is  picked  and 
shipped,  in  which  case 
a  lot  of  slightly  specked 
fruits  when  shipped 
may  arrive  as  mum- 
mies or  nearly  so. 

Cankers. — These  are 
diseases  that  arise  in 
connection  with  open 
wounds,  and  are  con- 
spicuous in  trees  (Fig. 
91).  Some  knowledge 
of  cankers  is  of  great 
practical  importance  in 
the  handling  of  forests 
and  orchards.  As  they 
are  wound  diseases,  it 
is  evident  how  the 
parasite  enters,  and  the 
wounds  are  formed  in 
nature  by  storms,  and 
in  cultivation  by  trimming  and  bruising.  If  the  wound  is 
small,  it  may  heal  naturally ;  but  if  it  is  large,  it  may  remain 
as  an  open  wound,  exposed  to  continuous  infection. 

Bitter  rot.  —  This  is  a  very  destructive  disease  of  apples 
and  other  fruits,  and  is  known  wherever  -apples  are  culti- 
vated. It  is  recognized  by  the  characteristic  spot  it  forms 
on  apples.  It  is  at  first  small,  increases  rapidly  in  size,  turns 


FIG.  91. —  Canker  on  apple  tree. — After  SORAUER. 


PLANT   DISEASES  443 

brown,  and  becomes  sunken  through  rotting  of  the  tissue 
(Fig.  92) .  These  spots  may  be  recognized  from  other  kinds  of 
spots  by  their  sunken  appearance,  their  bitter  taste,  and  their 
ringed  border.  This  disease  was  observed  for  many  years 
before  the  method  of  infection  was  discovered.  Now  it  is 
known  that  the  parasite  is  a  wound  parasite  that  develops 
cankers  on  the  twigs  (Fig.  93).  Abundant  spores  are  formed 
in  these  cankers  and  are  washed  down  by  rains  on  the  fruit 


FIG.  92.  —  Bitter  rot  of  apple.  —  After  CLINTON. 

below.  It  had  long  been  noticed  that  a  sudden  attack  of 
bitter  rot  was  brought  about  by  a  few  rainy  days. 

142.  Diseases  of  the  second  group.  —  In  this  group  of 
diseases  the  parasite  does  not  kill  living  cells,  but  lives  on 
their  products  and  often  induces  them  to  develop  unusual 
structures. 

Rust.  —  This  is  a  very  conspicuous  disease  of  cereals,  in 
which  the  parasite  and  host  live  peaceably  together  for  a 
time,  but  in  which  there  is  usually  no  abnormal  growth. 
The  "  disease,"  therefore,  consists  in  the  gradual  weakening 
of  the  living  cells  by  the  drain  upon  their  food  supplies, 
until  finally  they  can  work  no  more  and  are  destroyed  by 


444          '  ELEMENTARY   STUDIES   IN   BOTANY 

the  parasite.  It  is  easy  to  discover  this  trouble,  for  the  rusty 
patches  of  spores  become  abundant  on  the  leaves  and  stem 
of  the  host  plant,  but  the  cure  seems  hopeless,  and  preven- 
tion is  uncertain  as  yet. 

Crown  gall.  —  This  is  a  very  common  bacterial  disease  of 
trees  and  shrubs,  and  among  cultivated  plants  it  is  note- 
worthy in  the  various  fruit  trees  and  street  trees.  As  the 
name  implies,  the  symptom  of  the  disease  is  the  develop- 
ment of  a  gall-like  growth  (tumor)  on  the  "  crown  "  of  the 


FIG.  93.  —  Canker  of  bitter  rot  on  apple  twigs.  — After  BURRILL. 

plant,  which  means  the  base  of  the  stem  where  it  joins  the 
root  (Fig.  94).  During  the  autumn  and  winter  the  gall 
disintegrates  and  leaves  an  open  wound.  At  the  margin 
of  an  old  gall,  new  galls  arise,  and  so  the  wounds  are  en- 
larged from  year  to  year. 

A  most  interesting  fact  has  been  discovered  in  connection 
with  these  galls,  and  that  is  that  they  give  rise  to  a  disease- 
carrying  tissue  ("  infecting  strands ")  that  penetrates  to 
other  regions  of  the  plant  and  gives  rise  to  new  galls.  This 
makes  it  impossible  to  remove  the  trouble  by  surgery,  for 
while  galls  may  be  removed  and  the  wounds  healed,  the 
"  infecting  strands  "  are  spreading  the  trouble  into  other 
regions.  The  whole  trouble  begins  by  some  wounding  or 


PLANT   DISEASES 


445 


bruising  of  the  crown  that  permits  the  gall-forming  bacteria 

to  enter. 

Peach  leaf  curl.  —  It  is  a  frequent  trouble  in  peach  orchards 

that  the  leaves  become  curled  up  and  twisted  into  various 

shapes,  the  surface  looking 

wrinkled  and  blistered.  This 

interferes  with  the  work  of 

the    leaves    so    much    that 

there  may  be  an  extensive 

failure   of   the   crop.     This 

curling  and  twisting  is  due 

to  the  fact  that  the  presence 

of  the  parasite  causes  the 
leaf  cells  to  grow  very  un- 
evenly. 

Black  knot.  —  This  is  an 

exceedingly  common  disease, 
and  among  cultivated  plants 
it  is  most  commonly  seen  on 
plum  (Fig.  95,  a)  and  cherry 
trees,  but  it  is  common  also 
on  shrubs,  as  currants  (Fig. 
95,  6)  and  gooseberries.  It 
appears  as  small  hard  knots 
or  "  warts "  that  break 
through  the  bark  and  finally 
become  dark  brown  or  black. 
The  knot  is  made  up  of  a 
mixed  mass  of  cells  devel- 
oped by  the  host  plant  because  of  the  presence  of  the  fun- 
gus, and  interlaced  in  the  tissues  of  the  knot  is  the  thready 
body  of  the  parasite.  The  twigs  of  the  plant  may  not  be 
killed,  but  when  they  are  girdled  by  knots  they  are  destroyed. 
143.  Diseases  of  the  third  group.  —  In  this  group  of  dis- 
eases the  parasite  invades  the  water-conducting  vessels  and 


FIG.  94.  —  Crown  gall   on  daisy. — After 
ERWIN  SMITH. 


446 


ELEMENTARY   STUDIES   IN   BOTANY 


lives  in  the  sap,  cutting  off  the  water  supply  and  causing  the 
host  plant  to  wilt  and  die.  Since  the  first  symptom  of  the 
presence  of  these  parasites  is  the  wilting  of  the  host,  these 
diseases  are  known  in  general  as  "  wilts."  There  are  a  great 
many  kinds  of  wilt-producing  fungi,  but  their  relation  to  the 

host  and  their  effect  upon  it  are 
the  same.  A  few  illustrations 
will  be  given. 

Cabbage  wilt.  —  In  this  disease, 
the  water-conducting  vessels  are 
invaded  by  bacteria  that  enter 
through  the  "  water  pores  "  of 
the  leaves,  which  are  minute 
openings  along  the  edges  of  the 
leaves  that  are  connected  with 
the  system  of  water-conducting 
vessels.  They  are  in  fact  the 
open  terminals  of  this  system. 
The  disease  is  often  called  the 
"  black  rot  of  cabbage "  (Fig. 
96),  but  the  rotting  is  not  due 
to  the  wilt-producing  bacteria, 
but  to  the  decay  of  the  leaves 
or  of  the  whole  head  which  they 
have  been  the  means  of  killing. 

Cucurbit  wilt.  —  This  is  often 
a  very  destructive  disease  among 
In  this  case  there  is  no  natural 
opening  for  the  entrance  of  wilt-producing  bacteria,  as  in 
cabbage,  but  the  infection  is  through  wounds  produced  by 
the  bites  of  insects.  From  the  point  of  entrance  the  in- 
fection extends  through  the  vessel  system.  If  the  infection 
is  at  the  tip  of  a  branch,  the  wilting  is  gradual ;  if  it  is  in 
the  main  stem,  the  wilting  is  rapid. 

Fusarium  wilts.  —  Bacteria  are  not  the  only  fungi  that 


FIG.   95.  —  Black  knot:  a,  on  plum 
b,  on  currant.  —  After  MASSEE. 


melons   and   cucumbers. 


PLANT  DISEASES  447 

produce  wilt  diseases.  Among  the  other  wilt-producing 
forms  are  the  Fusariums.  Under  this  head  come  three  dis- 
eases of  great  importance  in  the  south,  namely  the  wilts  of 
cotton,  cowpea,  and  watermelon.  The  Fusarium  is  a  soil 
fungus,  so  that  the  infection  is  probably  what  is  called  a 
"  soil-infection,"  the  most  difficult  kind  to  guard  against. 


FIG.  96.  —  Black  rot  of  cabbage:  c,  healthy  plant;  s,  diseased  plant.  —After  HARDING. 

It  means  that  the  soil  of  a  field  becomes  infected,  and  that 
continued  planting  on  that  area  simply  increases  the  in- 
fected area  every  year.  Another  notable  Fusarium  wilt  is 
the  flax  wilt,  which  is  the  great  enemy  to  the  raising  of  flax. 
Fusarium-infected  soils  are  often  spoken  of  as  "  sick  soils," 
as  "  cotton  sick,"  "  flax  sick,"  etc. 

Mushroom  wilts.  —  These  are  our  most  important  tree 
diseases,  and  since  they  are  wood-destroying  diseases,  they 
are  of  great  importance  to  the  forester.  The  invading 


448 


ELEMENTARY    STUDIES   IN   BOTANY 


fungus  is  a  mushroom  (Fig.  97),  which  enters  the  tree  by  its 
spores  lodging  in  wounds,  or  penetrates  directly  into  the  tree 

by  way  of  the 
soil.  In  either 
event,  the  wood- 
vessels  are  in- 
vaded, and  the 
destruction  of 
wood  is  due  to 
the  action  of  sub- 
stances formed 
by  the  fungus. 
In  this  way  the 
various  "rots"  of 
trees  are  brought 
about. 

144.  Control  of 
diseases. — All  of 
the  study  of  plant 
diseases  has  for 
its  purpose  the 
control  of  dis- 
eases. It  is  evi- 
dent that  this  is 
a  vast  and  com- 
plicated subject. 
A  great  many 
"  treatments  "  are 
suggested  that 
are  not  based  in 
knowledge;  they 
may  do  good,  or 

they  may  be  useless.  Naturally,  people  use  any  treatment 
that  may  do  good,  rather  than  no  treatment  at  all.  But  as 
the  knowledge  of  plant  diseases  increases,  treatments  are 


FIG.  97. — Tree  fungus  on  aspen.  —  After  VON  SCHRENK 
and  SPAULDING. 


PLANT   DISEASES  449 

becoming  more  and  more  intelligent  and  effective.  There 
are  a  few  general  principles  that  lie  at  the  basis  of  any  intel- 
ligent and  effective  treatment,  and  these  principles  should 
be  known  to  all  who  cultivate  plants. 

145.  Infection.  —  No  intelligent  control  of  disease  is  pos- 
sible without  exact  knowledge  of  the  sources  of  infection. 
A  good  illustration  of  the  truth  of  this  statement  may  be 
obtained  from  the  case  of  peach  curl.     For  a  long  time  it  was 
supposed  that  the  infection  came  from  a  parasite  that  lived 
year  after  year  in  the  peach  tree,  and  therefore  that  no  control 
was  possible.     But  when  it  was  found  that  the  infection  came 
from  spores  that  lodged  on  the  buds,  thus  getting  a  chance 
at  very  young  leaves,  the  control  became  obvious  and  easy. 

It  is  well  to  recall  the  various  sources  of  infection  known, 
and  to  remember  that  they  are  not  yet  known  in  the  case 
of  most  diseases.  There  are  soil  infections,  the  parasites 
living  from  season  to  season  in  the  soil ;  spore  infections,  in 
which  spores  are  carried  by  the  wind,  by  insects,  by  rain- 
drops, by  seeds,  etc. ;  wound  infections ;  and  infections  by 
parasites  that  live  from  season  to  season  in  the  host.  There 
are  also  parasites  on  the  surfaces  of  host  plants,  and  para- 
sites within  the  tissues  of  host  plants;  the  former  can  be 
treated  easily,  and  the  latter  not. 

146.  Fungicides.  —  A  fungicide  is  a  substance  that  kills 
fungi.     It  is  applied  usually  either  as  a  powder  or  as  a 
liquid,  and  it  is  obvious  that  its  application  depends  upon 
whether  the  fungus  can  be  reached.     The  obvious  conditions 
for  application  are  when  the  parasite  is  a  superficial  one,  or 
when  its  spores  are  lodged  somewhere  on  the  surface  of  the 
plant.     Such  applications  are  clearly  not  appropriate  in  the 
case  of  soil  infections,  or  in  the  case  of  parasites  living  per- 
manently within  the  tissues  of  the  host.     It  should  be  remem- 
bered, also,  that  some  fungicides  injure  some  plants,  so  that 
their  use  upon  them,  no  matter  what  may  be  the  position  of 
the  parasite,  is  impossible. 


450  ELEMENTARY    STUDIES   IN   BOTANY 

The  list  of  fungicides  is  a  long  one,  and  would  not  be 
appropriate  here.  Their  names  and  their  composition  can 
be  obtained  easily  if  needed.  The  most  famous  and  the 
most  generally  useful  is  called  "  Bordeaux  mixture,"  which 
was  discovered  in  connection  with  the  ravaging  of  European 
vineyards  by  mildew.  It  is  a  mixture  of  copper  sulphate  and 
lime. 

When  it  is  discovered  that  a  fungicide  is  appropriate,  the 
next  thing  is  to  know  when  to  apply  it.  This  can  be  made 
plain  by  a  few  illustrations.  The  grape  mildew  infects  the 
grape-vine  by  means  of  its  spores  falling  upon  young  leaves. 
Accordingly,  the  young  leaves  are  sprayed  with  the  fungi- 
cide, and  this  treatment  has  proved  to  be  completely  effective 
in  controlling  the  disease. 

The  case  of  potato  disease  ("  potato  rot  ")  is  somewhat 
different.  Here  also  the  disease  is  spread  by  wind-blown 
spores,  which  infect  young  leaves.  Therefore,  early  spray- 
ing of  potato  plants  with  Bordeaux  mixture  checks  the 
spread  of  the  disease.  But  the  more  serious  trouble  comes 
from  the  infected  tubers  which  pass  the  disease  on  from 
generation  to  generation.  The  fungicide  treatment  in  this 
case,  therefore,  does  not  eliminate  the  disease,  but  simply 
checks  its  spread. 

In  the  brown  rot  of  stone  fruits,  the  infecting  spores  are 
lodged  on  the  bark  and  leaf  buds.  It  follows  that  these 
spores  should  be  destroyed  by  the  application  of  a  fungicide 
in  late  winter  or  early  spring.  In  brown  rot,  in  addition  to 
spores  lodged  on  bark  and  leaf  buds,  there  is  danger  of  infec- 
tion from  mummied  fruits  hanging  on  the  twigs  or  fallen  on 
the  ground,  and  it  is  evident  that  all  such  fruits  should  be 
destroyed. 

Of  course  the  powdery  mildews,  such  as  attack  grapes  and 
induce  a  skin  disease  of  the  fruit,  are  easily  reached  and 
killed  by  a  fungicide  while  the  fruit  is  young. 

These  illustrations  will  serve  to  indicate  what  is  meant 


PLANT  DISEASES  451 

by  the  statement  that  fungicides  are  appropriate  only  for 
certain  parasites ;  that  in  each  case  there  is  a  most  effective 
time  for  their  application ;  and  that  in  some  cases  they  are 
only  of  supplementary  use,  not  reaching  all  the  sources  of 
infection. 

147.  Surgery.  —  This  means  the  removal  of  infection  and 
guarding  against  further  infection.     Perhaps  no  treatment 
of  plants  is  done  more  thoughtlessly  and  needlessly  than 
surgery.     Before  any  such  operation,  one  must  be  sure  of 
three  things :    (1)  whether  the  infection  exists  in  the  part 
proposed  to  be  removed;    (2)  if  so,  whether  it  will  do  any 
good  to  remove  it ;   (3)  and  if  so,  whether  it  can  be  removed. 
A  few  illustrations  will  make  this  plain. 

In  the  case  of  pear  blight,  the  flowers  are  infected  by  in- 
sects that  obtain  the  bacteria  from  certain  affected  branches 
in  which  they  have  passed  the  winter.  It  happens  that 
these  branches  show  their  character,  for  they  are  "  blighted. " 
It  is  obvious  that  such  branches  must  be  pruned  out  before 
the  opening  of  the  flowers. 

Crown  gall  was  once  thought  to  be  a  case  for  surgery,  but 
now  it  is  shown  that  the  removal  of  a  gall  (tumor)  is  in- 
effective because  there  are  infecting  strands  (p.  444)  which 
cannot  be  removed.  This  illustrates  a  case  in  which  the 
infected  area  is  known,  but  it  cannot  be  removed.  The 
only  surgery  useful  in  crown  gall  is  to  destroy  all  affected 
nursery  stock. 

One  of  the  most  common  applications  of  surgery  is  in 
connection  with  the  treatment  of  wounds  on  trees,  to  prevent 
cankers  and  invasions  of  the  water-conducting  vessels.  A 
race  of  "  tree  surgeons  "  has  been  developed,  some  of  whom 
are  reliable,  and  others  are  ignorant  of  their  business.  The 
general  method  is  to  clean  out  the  wound  so  that  a  fresh 
surface  is  exposed  for  healing,  and  then  to  cover  it  so  as  to 
prevent  the  entrance  of  wound-infecting  fungi. 

148.  Soil  infection.  —  When  soil  infection  is  involved  in 


452  ELEMENTARY   STUDIES   IN   BOTANY 

any  disease,  it  is  peculiarly  hard  to  control.  Once  the  use 
of  soil  fungicides  was  recommended,  but  since  we  have 
learned  something  about  the  soil,  this  has  been  shown  to 
be  a  very  dangerous  proceeding.  The  soil  is  swarming  with 
bacteria  and  other  fungi,  many  of  which  are  extremely  im- 
portant, and  fungicides  cannot  pick  out  one  organism  for 
destruction  and  leave  the  others  alive.  Such  a  treatment  is 
much  like  annihilating  the  population  of  a  city  to  get  at 
one  criminal.  There  is  no  evidence,  as  yet,  that  any  so- 
called  soil  fungicide  does  any  good. 

If  fungicides  are  not  available  for  soil  infections,  such  as 
occur  in  numerous  wilt  diseases,  what  can  be  done?  In  the 
case  of  garden  crops,  as  cabbage,  infected  plants  can  be  re- 
moved or  destroyed,  but  in  the  case  of  field  crops  this  is 
impracticable.  The  only  known  method  of  controlling  soil 
infection  is  to  stop  planting  the  susceptible  crop  on  the 
infected  area,  and  to  plant  some  other  crop.  This  rotation 
generally  eliminates  the  infection  or  weakens  it. 

149.  Uninfected    stock.  —  In    all    cases    of   infection    by 
parasites  living  from  one  season  to  the  next  in  a  plant,  the 
only  safe  thing  to  do  is  to  see  to  it  that  seeds  or  tubers  or 
cuttings  used  in  propagation  are  obtained  from  absolutely 
uninfected  stock.     This  has  been  tried  with  the  potato  dis- 
ease and  found  to  be  most  effective. 

150.  Resistant  races.  —  The  breeding  of  races  of  plants 
resistant  ("  immune  ")  to  the  different  diseases  is  the  final 
resort  in  the  matter  of  control.     When  nothing  else  avails, 
the  cultivation  of  immune  races  must  be  resorted  to.     Prob- 
ably this  will  be  the  final  remedy  for  all  our  plant  diseases, 
but  those  that  can  be  controlled  can  afford  to  wait.     For 
this  reason,  the  work  on  resistant  races  as  yet  has  had  to  do 
chiefly  with  diseases  that  arise  from  soil  infections.     The 
following  illustrations  indicate  that  some  progress  has  been 
made. 

In  the  case  of  the  potato  disease  it  was  shown  how  a 


PLANT  DISEASES  453 

fungicide,  like  Bordeaux  mixture,  can  be  used  on  very 
young  plants  to  reduce  the  spread  of  infection  during  a 
growing  season ;  but  the  more  serious  trouble  is  in  the  soil, 
from  infected  tubers.  It  was  in  connection  with  this  im- 
portant disease  that  the  first  attempts  were  made  to  develop 
resistant  races,  and  many  have  been  obtained.  The  trouble 
has  been  that  resistant  races  do  not  continue  to  be  resistant, 
and  in  a  few  seasons  they  are  no  more  resistant  than  other 
races.  Also,  the  resistant  races  have  not  proved  to  be  re- 
sistant in  all  localities. 

In  the  case  of  the  Fusarium  wilts,  as  of  cotton,  the  cultiva- 
tion of  resistant  races  began  seven  or  eight  years  ago,  and 
in  four  or  five  years  success  was  attained.  Several  resistant 
races  of  cotton,  and  also  of  cowpea,  were  secured.  As  in 
the  case  of  resistant  races  of  potato,  however,  the  resistant 
races  of  cotton  have  not  always  retained  this  character  in 
all  localities. 

The  discovery  and  development  of  a  race  of  wheat  resist- 
ant to  rust  have  been  described  (p.  355). 

The  cultivation  of  races  resistant  to  disease  is  very  new 
work,  but  it  promises  to  be  the  method  by  which  we  shall 
finally  eliminate  all  the  diseases  of  cultivated  plants. 

151.  Suggestions  for  work.  —  Probably  no  work  can  be 
done  with  plant  diseases  except  in  learning  to  recognize  some 
common  diseases.  As  many  cultivated  plants  as  possible, 
including  street  trees,  should  be  examined  for  diseases, 
especially  for  spotted  leaves,  wilts,  galls,  black  knot,  and 
cankers.  All  wild  plants  are  subject  to  disease,  and  these 
might  be  used  to  extend  the  observations. 

In  addition  to  this,  specimens  showing  the  usual  diseases 
of  the  common  cultivated  plants  can  probably  be  obtained 
by  any  school  from  its  state  Agricultural  Experiment  Station. 
These  will  serve  as  valuable  guides  to  the  recognition  of  these 
diseases  among  the  plants  cultivated  in  the  neighborhood  of 
the  school. 
30 


INDEX 


Heavy  figures  indicate  pages  on  which  illustrations  occur. 


Acacia,  flower  of,  157. 

Adiantum,  90. 

Agave,  208. 

Agriculture,  296. 

Air-roots,  268j_269. 

Aleurone  grains,  177. 

Alfalfa,  364. 

Alga?,  8. 

Alternation  of  generations,  75. 

Althaea,  flower  of,  137. 

Angiosperms,  115,  129. 

Annual  rings,  239. 

Annuals,  238. 

Annular  vessels,  238. 

Anther,  123,  134,  135,  136. 

Antheridium,  27  ;    of  ferns,   99  ; 

of  liverworts,   74 ;    of    mosses, 

80. 

Anthoceros,  83,  84,  85. 
Apple,  390;    bitter  rot  of,  443, 

444 ;     canker    on,    tree,    442 ; 

flower  of,  156;    fruit  of,  149; 

spot  disease  of,  leaf,  434. 
Apricot,  393. 
Archegonium,    of   ferns,    98 ;     of 

liverworts,  75 ;    of  mosses,  80. 
Ascomycetes,  57. 
Aspen,  tree  fungus  on,  448. 
Aspidium,  92. 
Assimilation,  38,  176. 
Aster,  4(39,  490. 
Autumn  colors,  214.     • 
Axil,  226. 

B 


Bacteria,  43,  44. 
Bacteriology,  44. 


Bark,  240. 

Barley,  357,  358. 

Barley-production,  map  showing 
states  of  greatest,  357. 

Basidiomycetes,  58. 

Bast,  237. 

Bean,  167,  386;  germination  of, 
177,  178,  179,  180,  181,  323, 
324 ;  section  of,  319 ;  seed-dis- 
charge, 168. 

Beet,  374;  spot  disease  of,  leaf, 
438. 

Beggar-ticks,  173. 

Bilabiate,  134. 

Biology,  1. 

Bitter  rot,  442. 

Black  knot,  445. 

Bluebell,  133. 

Blue-green  Algae,  31. 

Brown  Algae,  31. 

Brown  rot,  441. 

Bryophytes,  7,  66,  114. 

Bud,  225. 

Budding,  332. 

Bulb,  250,  377. 

Bulblet,  250. 

Burdock,  174. 


Cabbage,  373,   378,  379;    black 

rot  of,  447. 
Cactus,  209. 
Cactus  deserts,  283. 
Calyx,  131. 
Cambium,  239. 
Cankers,  442. 
Canteloupe,  385. 
Capillary  movement,  314. 


455 


456 


INDEX 


Carbohydrate,  32,  35. 

Carbon  dioxide,  32,  303. 

Carnation,  404,  405. 

Carnivorous  plants,  218. 

Carpel,  120,  137. 

Carrot,  376. 

Catalpa,  seed  of,  171. 

Celery,  382. 

Cell,  9. 

Cellulose,  9. 

Cell-wall,  9. 

Cereals,  342. 

Chemistry  of  soil,  308. 

Cherry,  394. 

Chlorophycese,  31. 

Chlorophyll,  10,  33. 

Chloroplast,  10,  33. 

Chrysanthemum,  407. 

Cladophora,  16. 

Classification,  3. 

Climbers,  233. 

Clinging  roots,  268. 

Clover,  363,  364. 

Club-mosses,    88,    91,    95,    101, 

108. 

Cocklebur,  174. 
Coleochsete,  15. 
Colony,  12. 
Compass  plants,  211. 

Conifers,  116. 

Cork  cambium,  240. 

Corn,    137,   343,    344,    347,    348 
349,  350  ;  germination  of,  182 
section  of  a  grain  of,  318  ;  selec- 
tion, 347 ;   tester,  348. 

Corn-breeding,  337. 

Corn-production,    map    showing 
, states  of  greatest,  343. 

Corolla,  131. 

Cortex,  236. 

Cotton,  411,  412. 

Cotton-production,  map  showin; 
states  of  greatest,  414. 

Cotyledons,  126  ;   escape  of,  181 

Cow-pea,  365. 

Cross-pollination,  158. 

Crown  gall,  444. 


Cryptogams,  98. 
Cucumber,  384. 
Cultivated  plants,  296. 
Currant,    400;     black   knot    on, 
446 ;   spot  disease  of,  leaf,  436. 
Cuticle,  205. 
buttings,  326,  327. 

iyanophycese,  31. 
Cycads,  117. 
Cyclic  leaves,  229. 

iytoplasm,  10. 


Daffodil,  408. 

Dahlia,  254. 

Daisy,  crown  gall  on,  445. 

Dandelion,   fruit   of,    169;     root 

of,  253. 
Darlingtonia,  219. 
Deadnettle,  133. 
Deciduous  forest,  286,  287. 
Deciduous  habit,  214. 
Department  of  Agriculture,  333. 
Dicotyledons,  146. 
Digestion,  38,  176. 
Dionsea,  222. 
Diseases,  4,  41,  432 ;    control  of, 

448. 

Disease-resistance,  335. 
Dogtooth  violet,  153. 
Dormancy,  11. 
Dorsi ventral,  69. 
Dotted  vessels,  238. 
Dros.era,  220,  221. 
Drought,  294. 
Drought-resistance,  336. 
Dunes,  282,  283. 


E 


Ectocarpus,  21,  26. 

Egg,  25. 

Elm,  228. 

Embryo,   318;    of  Angiosperms, 

145  ;   of  Gymnosperms,  126. 
Embryo-sac,  142. 
Endosperm,     318;       of     Angio- 


INDEX 


457 


sperms,  167  ;  of  Gymnosperms, 

127. 

Energy,  34. 

Epidermis,  69,  192,  205. 
Epigynous,  156. 
Epilobium,  pollination  of,  163. 
Epiphytes,  269. 
Equisetales,  102. 
Equisetum,  100,  101,  107. 
Evergreen  habit,  215. 
Evolution,  4. 
Experiment  Stations,  334. 


Fats,  177. 

Ferns,  88,  90,  92,  102,  103,  104, 
105,  106,  107. 

Fertilization,  23 ;  in  Angio- 
sperms,  143 ;  in  Gymno- 
sperms, 125. 

Fibre  plants,  411. 

Fig  wort,  pollination  of,  162. 

Filament,  123,  134. 

Filicales,  104. 

Fireweed,  seed  of,  170. 

Flax,  414,  415. 

Flora,  8. 

Floriculture,  297,  401. 

Flowers,  130,  401 ;  evolution  of, 
151. 

Food  manufacture,  31. 

Food  problem,  340. 

Food  storage,  177. 

Foot,  76. 

Forage  plants,  362. 

Forestry,  5,  419. 

Forests,  care  of,  422;  character 
of,  420;  and  floods,  421;  for- 
mation of,  421 ;  products  of, 
424 ;  protection  of,  423  ;  reser- 
vations, 427. 

Forest  succession,  277. 

Fruit,  147,  383,  387. 

Fucus,  17,  26,  27,  28. 

Fungi,  40. 

Fungicides,  449. 

Funiculus,  141. 


Gametangium,  26. 
Gamete,  23. 

Gametophore,  77,  78,  79. 
Gametophytes,  76,  110,  111;  of 

Angiosperms,    141  :    of   Ferns, 

98 ;     of    Gymnosperms,     123, 

124. 

Gardening,  368. 
Gemmae,  73. 
Geotropism,  179. 
Germination,  22  ;  of  seeds,  174. 
Germinator,  seed,  321,  322,  324. 
Girdling,  240. 
Gloeothece,  12,  13. 
Gloeotrichia,  13,  14. 
Gooseberry,  400. 
Gourd  family,  384. 
Grafting,  241,  330.  331,  332. 
Grape,  396 ;  spot  disease  of,  leaf, 

439. 

Grape-fruit,  395. 
Grass  family,  362. 
Green  Algse,  31. 
Guard-cells,  193. 
Gymnosperms,  114,  115. 

H 

Habit,  224. 
Habitat,  273. 
Hairs,  206,  207. 
Haustoria,  46. 
Heart  wood,  243. 
Heat,  301. 
Hemp,  416. 
Heredity,  5. 
Heterospory,  108. 
Homospory,  108. 
Horsetails,  102. 
Horticulture,  297. 
Host,  41. 

Houstonia,  flower  of,  164 ;    pol- 
lination of,  163. 
Hybridization,  338. 
Hydrophytes,  279. 
Hydrotropism,  180. 


458 


INDEX 


Hypocotyl,  126,  185 ;    escape  of, 

177. 
Hypogynous,  156. 


Infection,  449. 

Inorganic,  32. 

Insectivorous  plants,  218. 

Insect-pollination,  158. 

Integument,  123. 

Internodes,  224,  326. 

Involucre,  380. 

Iris,    flower  of,  158 ;   pollination 

of,  160. 

Irregularity,  133,  156. 
Irritability,  179. 


Jonquil,  408. 


Laminaria,  16. 

Layering,  232,  329. 

Leaf,  89,  187,  188;  compound, 
190  ;  mosaic,  201,  202,  203  ;  sec- 
tion of,  191 ;  skeletonized,  189. 

Leaflet,  191. 

Leaves,  as  vegetables,  378. 

Legume  family,  363. 

Legumes,  385. 

Lemon,  395. 

Lettuce,  380,  381. 

Lichens,  58,  59,  60,  61. 

Life  of  soil,  310. 

Life-relations,  5. 

Light,  301. 

Lily,  anther  of,  135. 

Limiting  factors,  30Q. 

Linseed  oil,  415. 

Liverworts,  67. 

Lycopodiales,  101. 

Lycopodium,  95. 

M 

Macrocystis,  16. 
Maple,  fruit  of,  170. 


Maple  leaf,  spot  disease  of,  435. 
Marchantia,  69,  70,  71,  73,  74, 

75. 

Mass  culture,  334. 
Meadows,  284,  285. 
Megasporangium,  108,  109. 
Megaspore,  108. 
Megasporophyll,  108,  109. 
Mesophyll,  194. 
Mesophytes,  279. 
Micropyle,  123. 
Microsporangium,  108,  109. 
Microspore,  108. 
Microsporophyll,  108,  109. 
Midrib,  189. 
Mildews,  437  ;  downy,  47,  48,  49  ; 

powdery,  49,  50. 
Milkweed,  seed  of,  170. 
Molds,  46. 

Monocotyledons,  145. 
Mosses,  77. 

Motile  leaves,  212,  213. 
Mucor,  45,  46,  47. 
Mushrooms,  53,  54,  55,  56,  57. 
Muskmelon,  384. 
Mycelium,  46. 
Mycorhiza,  64. 

N 

Narcissus,  408. 
Nectar,  159. 
Nepenthes,  219. 
Nereocystis,  17. 
Nitrogen,  303. 
Nodes,  224,  326. 
Nostoc,  12,  14. 
Nucellus,  123. 
Nucleus,  10. 
Nutrition,  2,  11. 

0 

Oak,  229. 

Oat-production,     map     showing 

states  of  greatest,  351. 
Oats,  351,  352,  353. 


INDEX 


459 


(Edogonium,  20,  21. 

Oils,  177. 

Onion,  377. 

Oogonium,  27. 

Oospore,  23. 

Orange,  394. 

Orchard  fruits,  389. 

Orchards,  389. 

Orchid,  flower  of,  161 ;  pollina- 
tion of,  161. 

Organic,  32. 

Oscillatoria,  13,  14. 

Osmosis,  264. 

Ovary,  138. 

Ovule,  of  Gymnosperms,  120, 
122 ;  of  Angiosperms,  140. 

Oxygen,  300;  as  a  by-product, 
36. 


Palisade  cells,  194,  206. 
Palmate,  189. 
Pansy,  405,  406. 
Parallel-veined,  189. 
Parasite,  40. 
Parsnip,  376. 
Peach,  148,  389,  392. 
Peach  leaf  curl,  445. 
Pear,  388,  391. 
Pear  blight,  435. 
Peas,  386. 

Pedigree  culture,  335. 
Peony,  131. 
Perennials,  238. 
Perianth,  130,  131. 
Perigynous,  156. 
Petal,  132. 
Petiole,  187. 
PhaeophycesB,  31. 
Phloem,  237. 
Phlox,  133. 
Phosphorus,  304. 
Photosynthesis,  34,  195. 
Phototropism,  183. 
Phycomycetes,  57.  • 
Physics  of  soil,  309. 


Pine,  227. 

Pineapple,  149. 

Pine   needles,    21^;     section   of, 

215. 

Pinnate,  189. 
Pistil,  139. 

Pitcher-plants,  218,  219. 
Pith,  236. 
Pith  rays,  237. 
Plains,  283. 

Plant  associations,  272. 
yiant-breeding,  5,  164,  333. 
•Plant  succession,  276. 
Plastid,  33. 
Pleurococcus,  12. 
Plum,  393 ;   black  knot  on,  446. 
Plume,  126;   escape,  181. 
Pods,  of  iris,  147 ;   of  sweet  pea, 

146. 

Pollen,  121. 
Pollen  sac,  135. 
PoUen  tube,  125. 
Pollination,     125 ;      by    insects, 

158. 

Polypetalpus,  133. 
PoreUa,  72. 
Potato,   369,   370,   371;    disease 

of,  440,  441 ;    tuber,  328. 
Potentilla,  230;    flower  of,   156. 
Prairies,  284. 
Profile  leaves,  211. 
Prop-roots,  265,  266,  267. 
Protective  positions,  210. 
Protective  structures,  204. 
Protein,  37. 
Protoplasm,  9. 
Protoplast,  9. 
Pteridophytes,  7,  88,  114. 
Pumpkin,  385. 


R 


Radish,  254,  372,  374. 
Rain,  protection  against,  209. 
Raspberry,  391,  399. 
Reaction,  185. 
Receptacle,  152. 


460 


INDEX 


Red  Algse,  31. 

Reed  swamp,  280. 

Regular,  133. 

Reproduction,  2,    11 ;    in  Algae, 

17 ;    in  Liverworts,  73. 
Resistance,  452. 
Respiration,  36,  38,  175. 
Response,  178. 
Rhizoids,  71. 
Rhodophyceae,  31. 
Ribs,  189. 
Riccia,  68. 
Rice,  360,  362. 
Rice-production,     map    showing 

states  of  greatest,  361. 
Root,  94,  253,  372  ;  development 

of,  180 ;   structure  of,  256. 
Root-cap,  255. 
Root-hairs,  256. 
Root-pressure,  244. 
Rootstock,  247,  248. 
Rose,  403,  404. 
Rosette-habit,  199,  200,  211. 
Rotation  of  crops,  363. 
Rust,  51,  52,  443. 
Rye,  359,  360. 
Rye-production,     map     showing 

states  of  greatest,  359. 


8 


Salts,  movement  of,  in  soil,  315.' 

Sap,  ascent  of,  242. 

Saprophyte,  40. 

Sap  wood,  243. 

Sargassum,  18. 

Sarracenia,  218. 

Scales,  216. 

Seed,  126,  317;  of  Angiosperms, 
147 ;  box  for  germination  of, 
324  ;  dispersal,  169  ;  germina- 
tion of,  174,  320;  of  Gym- 
nosperms,  127;  selection  of, 
319. 

Seed-firms,  333. 

Selaginella,  91,  108,  111. 

Self-pollination,  158. 


Senecio,  fruit  of,  169. 

Sensitive  plant,  212. 

Sepal,  131. 

Sex,  differentiation  of,  25 ;  ori- 
gin of,  23. 

Sex-organs,  26. 

Shading,  projection  against,  199.. 

Shasta  daisy,  403. 

Sieve  vessels,  238. 

Smilax,  225. 

Snapdragon,  133. 

Snowflake,  157. 

Soil,  259,  298,  308. 

Soil  fungi,  61. 

Sorus,  96,  97,  98. 

Spanish  needles,  173. 

Spermatophytes,  7,  114,  129. 

Sperms,  25  ;   of  Cycads,  125. 

Spiral  leaves,  228. 

Spiral  vessels,  237. 

Spirogyra,  27,  29. 

Spongy  tissue,  194. 

Sporangium,  22  ;  of  Ferns,  96,  97. 

Spore,  21. 

Sporophore,  47. 

Sporophyll,  97. 

Sporophyte,  76,  81,  83;  of 
Angiosperms,  130 ;  of  Gym- 
nosperms,  118. 

Spot  diseases,  434,  435,  436,  437, 
438,  439. 

Squash,  385. 

Stamen,  121,  123;  of  Angio- 
sperms, 134. 

Stem,  93,  224 ;  structure  of,  235. 

Stigma,  138. 

Stimulus,  178. 

Stomata,  192,  193. 

Stone-fruit  diseases,  441. 

Storage  form,  36. 

Strawberry,  391,  398;  spot  dis- 
ease of,  leaves,  437. 

Strawberry-plant,  231. 

Street  trees,  428 ;  care  of,  430. 

Strobilus,  104 ;  of  Gymno- 
sperms,  118,  119,  120,  121, 
122. 


INDEX 


461 


Style,  138. 

Substratum,  69. 

Subterranean  stems,  245. 

Summaries,  Algae,  30 ;  Angio- 
sperms,  148  ;  Bryophytes,  87  ; 
dispersal  and  germination  of 
seeds,  185 ;  the  flower  and 
insect-pollination,  165 ;  food- 
manufacture,  39  ;  Fungi,  64  ; 
Gymnosperms,  128 ;  leaves, 
222  ;  plant  associations,  289  ; 
Pteridophytes,  112;  roots, 
269 ;  stems,  251. 

Sundew,  220,  221. 

Surgery,  451. 

Swamp  forest,  281. 

Sweet  corn,  350. 

Sweet  pea,  406;  pollination  of, 
160. 

Sweet  potato,  375,  376. 

Sympetalous,  133,  154. 


Tap-root,  255. 

Tendrils,  216,  217,  246. 

Testa,  127,  167,  317. 

Thallophytes,  6,  8,  40,  114. 

Thorns,  217,  245. 

Tillage,  312. 

Toadflax,  133. 

Tobacco,  flower  of,  132. 

Tomato,  383. 

Toxic  substances,  305. 

Tracheary  vesselsi237. 

Transfer  form,  36. 

Transpiration,  195. 

Tropical  forest,  288. 

Tube  nucleus,  141. 

Tuber,  249,  369;   potato,  328. 

Tulip,  409. 

Tumbleweed,  172. 


Turgor,  10. 
Turnips,  373,  374. 

U 

Ulothrix,  15,  16,  21,  23. 


Vascular  bundles,  237. 
Vascular  cylinder,  93,  94,  236. 
Vascular  system,  89. 
Vaucheria,  27,  28. 
Vegetables,  367. 
Vegetative  multiplication,  18. 
Vegetative  propagation,  326. 
Veins,  90,  195. 
Venus  fly-trap,  222. 
Viability,  318. 

Violet,  405 ;  seed  of  a,  317 ;  seed- 
discharge,  168. 

W 

Water,  302 ;  movement  of,  in 
soil,  314. 

Watermelon,  385. 

Water  roots,  266. 

Water  storage,  208. 

Wheat,  354,  355,  356. 

Wheat-production,  map  show- 
ing states  of  greatest,  364. 

Wheat  rust,  51,  52. 

Wild  wheat,  355. 

Wilts,  446. 

Wood,  237. 

Woodbine,  234,  235. 

X 

Xerophytes,  279. 
Xylem,  89,  237. 


NATURE  STUDY  AND  AGRICULTURE 

Practical  Nature  Study  and  Elementary 
Agriculture 

A  Manual  for  the  Use  of  Teachers  and  Normal  Students. 
By  JOHN  M.  COULTER,  Director  of  the  Department  of 
Botany,  University  of  Chicago;  JOHN  G.  COULTER^ 
Professor  of  Biology,  Illinois  State  Normal  University ; 
ALICE  JEAN  PATTERSON,  Department  of  Biology,  in 
charge  of  Nature  Study,  Illinois  State  Normal  University. 
1 2 mo,  cloth,  $1.35  net. 

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CHEMISTRY  FROM  A  NEW  STANDPOINT 

An  Inductive  Chemistry 

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TWENTIETH  CENTURY  TEXT-BOOKS 

A  High  School  Course  in  Physics 

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TWENTIETH  CENTURY  TEXT-BOOKS. 


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Entrance  Requirements  to  the  National  Educational  Association  in 
1899.  It  keeps  accurately  to  the  definition  laid  down  ;  it  furnishes  the 
requisite  kind  and  amount  of  instruction  to  train  the  observation  and 
to  prepare  for  later  special  courses  in  science  ;  and  it  elevates  physical 
geography  beyond  cavil  to  the  proper  plane  for  a  college-entrance 
requirement,  by  organizing  its  content  to  its  highest  capacity  as  a 
pedagogic  discipline. 

D.    APPLETON    AND    COMPANY,     NEW    YORK. 


An  Elementary  Commercial  Geography. 

By  CYRUS  C.  ADAMS,  B.A.,  F.A.G.S.,  Presi- 
dent of  The  American  Geographical  Society ; 
Author  of  "A  Text-Book  of  Commercial 
Geography  "  (Twentieth  Century  Text-Books). 
1 2  mo.  Cloth,  $1.10. 

There  are  obvious  reasons  for  teaching  elementary 
commercial  geography  in  grammar  schools.  The  great 
majority  of  pupils  never  reach  the  high  schools  ;  conse- 
quently courses  of  study  for  the  grammar  schools  should  in- 
clude not  only  "reading,  writing,  and  arithmetic,"  the  ac- 
cepted disciplinary  studies,  but  also  studies  that  give  valu- 
able practical  knowledge  to  the  boys  and  girls  who  are  to 
enter  business  life  at  an  early  age,  studies  that  are  of  value 
because  of  the  moment  of  their  subject-matter.  The  interests 
of  this  country  are  so  broadly  business  interests,  the  personal 
interests  of  millions  of  our  people  are  so  intimately  con- 
nected with  the  products,  industries,  and  trade  of  the  country, 
that  commercial  geography  may  logically  demand  a  place  in 
the  elementary  school  course  from  the  value  of  what  it 
teaches. 

This  text  is  a  valuable  aid  to  a  practical  education,  as 
it  Americanizes  a  boy  and  provides  him  with  just  the  equip- 
ment essential  for  success  in  a  business  country. 

It  brings  out  the  commercial  powers  of  the  United 
States  in  a  way  that  is  entirely  within  the  realization  and 
intelligence  of  the  grammar-school  maturity. 

D.     APPLETON      AND      COMPANY, 

NEW  YORK.  BOSTON.  CHICAGO.  LONDON. 

2??e 


ANCIENT  HISTORY  FOR  THE  HIGH  SCHOOL 

The  Story  of  the  Ancient  Nations 

By  WILLIAM  L.  WESTERMANN,  Associate  Pro- 
fessor in  History,  University  of  Wisconsin.  Illus- 
trated. 1 2 mo,  Cloth,  $1.50. 

There  is  no  other  branch  of  history  taught  in  our  High 
Schools  in  which  so  much  new  material  has  come  to  light 
during  recent  years  as  in  ancient  history.  Much  of  the  best 
source  material  is  not  available,  in  translated  form,  to  the 
teacher.  This  text-book  has  been  written  with  the  desire  to 
put  into  the  hands  of  High  School  teachers  and  pupils,  in 
simple  and  concrete  form,  the  story  of  the  development  of 
ancient  civilization  as  it  appears  in  the  light  of  the  historical 
material  recently  discovered.  It  is  the  outcome  of  more  than  a 
decade  of  teaching,  both  in  High  School  and  University  classes. 

The  attempt  has  been  made  to  present  the  progress  of 
ancient  civilization  as  a  continuous  and  unified  process. 
There  has  been  included,  in  simple  terms,  as  much  of  the 
business  and  social  background  as  space  would  permit. 

The  language  of  the  book  is  clear  and  succinct.  The  order 
of  presentation  is  logical,  and  the  correlation  of  facts  exact. 
There  are  exceedingly  helpful  and  well-written  generaliza- 
tions, giving  the  significance  of  the  various  periods. 

There  are  plentiful  maps  throughout  the  book.  The  illus- 
trations, with  the  exception  of  a  few  carefully  selected  restora- 
tions, are  almost  entirely  drawn  from  ancient  sources.  They 
have  been  carefully  chosen  for  the  light  which  they  throw  on 
the  life  of  the  people. 

D.    APPLETON     AND     COMPANY 

NEW  YORK  CHICAGO 

504e 


THE  FOURTH 
SEVENTH     DAY 


OCT  31 1932 

*     FEB  6    1939 


jyt  861958 


2l-3m-6,'32 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


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